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Home , Phytogeography, Plant taxonomy

Acta Bot. Neerl.39(3), September 1990, p. 305-320

Meetings of the Royal Botanical Society of

The

MEETING OF THE SECTION FOR MORPHOLOGY,

ANATOMY AND CYTOLOGY ON 1 DECEMBER 1989

Organization of Microfibrils and cells have a random texture. Since the authors men-

tioned above also found a random orientation of Cortical Microtubules in the Apex microtubules in the conclusion is corpus cells, our M.M.A. Sassen and A.M.C. Wolters-Arts.

that no co-alignmentoccurs between microfibrils and Department of Experimental , University of microtubules in these cells. corpus Nijmegen, Toernooiveld,6525 ED Nijmegen,The

Netherlands Freeze SubstitutionofMature Papaver The arrangement of cellulose microfibrils (CMFs) is rhoeas different in various of the shoot anti- regions apex: A.C. Van Aelst and M. Cresti 1 . Department of Plant clinal in tunica cells, random in corpus cells and trans- Cytology and Morphology, Wageningen verse in cells of the rib (Sakaguchi el al. AgriculturalUniversity, Arboretumlaan 4, 6703 BD Planla 1988, 175: 403-411). These data are based on Wageningen, The Netherlands, and 'Dipartimento di examinations of cryosections of Vinca major apices BiologiaAmbientale,Universita di Siena, Via P.A. with the polarizing microscope. Careful examination Mattioli 4, 53100 Siena, Italy with EM on Petunia and Vinca apices confirmed the

above for tunica and rib meristem but Fast in used findings cells, a freezing liquid propane was to create an

different type ofCMF arrangement was found for the absolute moment fixation of all cell constituents.

cells. Water inside and outside the cells into the corpus changed

Apices of Petunia hybrida and Vinca major were vitrified solid state. Freeze substitution in acetone or

fixed with a mixture of p-formaldehyde and glutar- methanol, in which 2% osmium tetroxide and 1%

aldehyde, and embedded in polyethylene glycol. uranylacetate is dissolved,was carried out in a special

sections 5 in thickness freeze substitution device Longitudinal pm were selected, (CS auto, Reichert) at

transferred to nickel oyster grids and extracted with — 80°C.

hydrogen peroxide and glacial acetic acid for 30 min at Three fixation procedures were compared. A con-

90°C. After rinsing with water the grids were covered ventional chemical fixation in water and two freeze

with a forravar film, air-dried, shadowcasted with substitution procedures (acetone and methanol),

platinum, and studied with TEM. resulted in striking differences in electron microscopi-

In corpus cells microfibrils aredepositedin lamella- cal images. In freeze-substituted material, structures

like sheets, each of which consists of parallel-oriented containing carbohydrates were highly contrasted,

CMFs. Microfibrils of adjacent lamellae are some- while (phospho)lipid-containingstructures were elec-

times interwoven, which means that these lamellae are tron transparent. The conventional chemical-fixed

depositedmore or less at the sametime but in different material showed the opposite: a high contrast of struc-

directions. Dependingon the number of divisions and tures with a (phospho)lipidorigin and electron trans-

on the direction of division, corpus cell walls consist parency of the carbohydrate-containing structures.

of varying numbers of lamellae. Near the pit fields, Substitution fluids are organic solvents which

microfibrils in onelamella deviate, which supports the have to dehydrate the cell cytoplasm and by

idea of a random orientation of CMFs. The orien- dissolving the ice followed by the diffusion of water

tation ofCMFs in tunica cells is parallel to the newly molecules. In order to fix and create contrasted struc-

formed cell wall, i.e. anticlinal. Cell walls of the rib tures inside the cell, a reaction of (glyco)proteins,

meristem show parallel-oriented microfibrils perpen- (phospho)lipids and carbohydrates with osmium

dicular to the direction of extension of these cells. tetroxide and uranyl acetate has to take place. Un-

As the direction of microfibrils is different for each fortunately, these chemical fixatives start reacting at

lamella,it is understandable that the average arrange- about — 60°C. This meansthat duringthe substitution

is — selective of ment, as seen with the polarizing microscope, procedure at 80°C a extraction cell

random. TEM studies, however, show that the newly constituents occurs.

synthesized CMFs in Petunia and Vinca corpus cells It is concluded that chemical fixation and freeze

in less This are deposited more or parallel arrays. con- fixation followed by dehydrationprocedures result in

tradicts the generally accepted view that meristematic different electron microscopical images which are

305 306 MEETINGS

additional to each other in the visualization of the by the plasmalemma. It is attached to the cell wall by a

ultrastructure of plant cells. cupule, a bell-like protrusion of the inner wall layer.

The contain small plastoglobuli, presumably

oil. Larger oil droplets appear loosely scattered in the Experimental Manipulation ofthe Plane of cytoplasm and often situated near the oil cavity, where Cell Division by Wounding they apparently pass through the plasmalemma sur- C.J. Venverloo. DepartmentofPlant Molecular rounding the oil cavity. Two specific cell organelles, Biology, University of Leiden, Nonnensteeg 3, 2311 not reportedpreviously for oil cells, occur in this stage: VJ Leiden, The Netherlands smooth tubular endoplasmic reticulum,appearing as

bundles of linearly arranged tubules, and groups of In vacuolated cells a phragmosome (PS) is formed

crystalline bodies, which are probably of protein- before mitosis. The PS is a thin cytoplasmic sheath

aceous In the course of 3 the thickness of that is positioned at the site of the future cell wall. One origin. stage

the inner wall layer, the relative volume of the oil of the functions of the PS is to guide the cell plate cavity, and cell size increase. duringcytokinesis. The question is whether the plane

of cell division becomes fixed before or during the

formation of a PS. The cells of small DistributionofNon-Articulated Branched explants of Nautilocalyx divided periclinally, Laticifers ofMorus nigra L. (Moraceae)

transversely or longitudinally. When the explants R.W. den Outer and W.L.H. van Veenendaal.

into cut, were separated two parts by a longitudinal Department of Plant Cytology and Morphology,

most cells near the wound divided longitudinally. WageningenAgricultural University, before Cells which had a non-longitudinalPS already Arboretumlaan 4,6703 BD Wageningen,The different the wound was made showed reactions: all Netherlands

cells at some distance (100-150 pm) from the wound The origin, development and arrangement of the and half of the cells close to the wound (0-100 pm) branched, non-articulated laticiferous system of divided in accordance with the PS. In some ofthe cells nigra L. (Moraceae) were studied. , close to the wound the original PS was replaced by a

seedlings, leaves, stems and ofyoung and mature longitudinal PS and a longitudinal cell wall was were investigated using light and scanning formed. In some other cells the original PS was more electron There laticiferous microscopy. are two sys- or less disturbed and an obliquecell wall was formed. tems present in the older plant, a primary and a These results show that the planeof cell division can secondary one.The primary laticifers arise from eight easily be changed in cells without a PS, but that a ini tials in the outer ofthe future it periphery procambium strong signal is needed to change in cells with a PS. near the cotyledonary node ofthe young heart-shaped In the last case a new PS is formed. This suggests that the first-formed . They produce transport sys- the plane of cell division is being fixed during PS for- tem of the plant. No additional primary laticifers are mation, not earlier (a full account of this study has formed in other primary tissues. Secondary laticifers been submitted to Protoplasma). of the same type as the primary onesare produced by

initials of the vascular cambium in stem and .

An Ultrastructural of the Study Their number is larger and variable. No fusions of

Development of Oil Cells in Annona laticiferous cells with one another or adjoining paren-

muricata chyma cells were observed. The extremely elongated,

branched laticiferous cells devoid of M E. Bakker. Rijksherbarium, PO Box 9514, 2300 thin-walled, are

exhibit combination ofintrusive and RA Leiden, The Netherlands pits. They a sym-

plastic growth; penetrations of other cells were not

The ultrastructure of developing and mature oil idio- Laticifers observed. are present in all vegetative tissues

blasts in the shoot and leaves of Annona apex with the exception of epidermis, and primary and has been studied with muricata (Annonaceae) light, secondary xylem. The close developmentaland distri- fluorescence and transmission electron microscopy. butional relationship between laticifers and phloem

Three developmental stages can be recognized. suggest a possible functional relationship.

Stage I. The small cells do not differ from the sur-

rounding cells by their size, but can be recognized by Anatomical Research—its Current their less electron-dense cytoplasm, plastids lacking Status thylakoids, and devoid of deposits. Stage 2 P. Baas. Rijksherbarium/Hortus Botanicus, PO Box resembles stage 1, but in the cells a suberized layer has 9514, 2300 RA Leiden, The Netherlands. been deposited against the initial cell wall. In the cells

of stage 3 an additional layer has been deposited An analysis of the literature database,

against the suberized layer: the inner wall layer. The maintained at the Jodrell Laboratory,Royal Botanic

Kew cells in stage 3 also contain an oil cavity, surrounded Gardens (UK) by Miss Mary Gregory, revealed MEETINGS 307

that the number ofwood anatomical publications per relation to pollution also dramatically increased in

5-year period had substantially increased between number. Studies on xylem development declined in

1965 and 1985 but now shows a slight decline. System- number over the last 5-year period, although

atic wood anatomy and other classical aspects ofcom- important new developments can be registered in parative wood anatomy mirror this overall trend and terms of integrative morphogenetic hypotheses. The have profited from a renewed interest with the advent number ofpublicationson wood identification fluctu-

of scanning electron microscopy. Ecological wood ates over the past 25 years; standardization of wood anatomy provides one of the causal explanations of anatomical features and international co-operationin wood structural diversification in plant and establishing computerized databases are majorrecent shows a steep increase in number ofpublicationsover developments. the last 25 The functional wood Studies years. same applies to to explain or predict physical and mechan- anatomy, although the total number of studies on ical properties from wood structure seemtolag behind hydraulic architecture and metabolic and defence these increases in publications on botanical aspects of functions of wood in is still disappointing. wood anatomical diversity (see also Baas, P, IA WA

Publications ongrowthrings and on wood structure in Bull. n.s. 1989,10:333-334).

MEETING OF THE SECTION FOR PLANT SYSTEMATICS AND

GEOGRAPHY ON 24 NOVEMBER 1989

Taxonomy and of clinal differentiation in shoot dimorphismfrom very high in Pinus to virtually absent in Abies, Picea and 11 Genera in Pinaceae

Pseudotsuga with discovered or , newly (Cathaya) A. Farjon. Institute ofSystematic Botany, University recognized (Nothotsuga, Hesperopeuce of Page, 1988) of Utrecht, Heidelberglaan2, PO Box 80.102, in intermediate positions. Moreover, this Utrecht, The Netherlands genera classification is in conflict with most other characters

The Pinaceae is, with c. 220 , the largest evaluated. A new classification is therefore proposed

of present-day . Several species of the larger (see also Frankis, Notes Roy. Bot. Card. Edinb. 45(3),

three dominate the boreo-montane of 1989: genera 527-548).

the northern The of and hemisphere. majority genera Pinoideae with Pinus species, however, must be regarded as more or less Piceoideae with genus Picea rare palaeoendemics with more extensive ranges in Laricoideae with genera Cathaya, Pseudotsuga and time. work all Tertiary Monographic on genera except Larix Pinus has led to a revised classification, based on Abietoideae with genera Cedrus, Abies, Pseudolarix, phenetic comparison of 25 characters ranging from Keteleeria, Notholsuga and Tsuga chemistry (e g. immunology) and karyology to

and morphology. The author anatomy present Within Laricoideae, Pseudotsuga and Larix are

11 in three of which accepts genera Pinaceae, are closely related, within Abietoideae Cedrus and Abies,

A review ofthe Tournefort’s monotypic. long (since and Pseudolarix, Keteleeria and Nothotsuga form

of the conifers Tnstitutiones', 1694) history grouping natural groupings. The family as a whole divides in

shows considerable variations of the opinion up to two: an ‘abietoid’ (Abietoideae) and a ‘pinoid’ group

present day. Despite criticisms, Pilger’s system (in of confirms this genera. Phytogeography generally ‘Die naiuflichen Engler and Prantl: Pflanzenfamilien’, modernized classification, which forms the taxonomic

2nd edn. 1926) is still widely used in modern text- ‘ ’ framework of a monograph: Pinaceae (approxi-

books. This nine in Pinaceae system groups genera as 340 with 118 and 123 mately pages, plates maps) follows version, (revised 1954). to be published in 1990 by Koeltz Scientific Books,

Koenigstein, FRG. Pinoideae with Pinus genus

Larix Laricoideae with genera Cedrus, and Pseudo-

larix and Stomata in Connaraceae Abietoideae with Systematics genera Abies. Keteleeria, Picea, C.C.H. Jongkind, Department of Plant , Pseudotsuga! ;and Tsuga Gen. Foulkesweg 37, Wageningen, The Netherlands

The dividing characters are dimorphism (Pinus)

and shoot in Pinoideae and In Connaraceae the of the and the dimorphism (all genera shape stomata

Close of this reveals formed the cells Laricoideae). scrutiny anentirely pattern by surrounding epidermis 308 MEETINGS

are useful taxonomic characters. This pattern and labels and preferably add representative wood the shape of the outer stomatal ledge show a large samples. variation within the family. They are, however, often

within each Both charac- surprisingly constant genus. Clonal Diversity in some Microspecies of ters are rather easy to recognize and this enables us to use them in combination with other leaf characters, Section Palustria (Lindb. fil.)

sterile down the and in to identify samples to genus Dahlst from Czechoslovakia and The

instances even to the species level. Patterns of many Netherlands neighbouringcells also reflect affinities between taxa. J. Battjes, S.B.J. Menken, Y. de Jong and H.J.M. den The most common and probably most primitive Nijs. Hugo de Vries Laboratory, Kruislaan 318, 1098 pattern in Connaraceae is that in which the stomata SM Amsterdam, The Netherlands four to are surrounded by seven epidermis cells

distinct orientation. the other The Taraxacum forms in lacking a Compared to genus a polyploid complex epidermis cells, the size of the cells surrounding the Europe. Diploids are mainly restricted to the southern

stomatamay be smaller (cyclocytic) equal to (anomo- parts of the widespread distribution area, whereas

cytic) or larger (actinocytic). These three types are not agamospermic polyploids are found throughout. sharply delimited and gradual transitions occur Among the polyploid microspecies, taxa with either between them in Connaraceae, particularly between obligate or facultative agamospermy are known. the first These for all two types. patterns are typical Isozyme electrophoresis was used to determine clonal

of the tribes Connareae = in from the section genera ( Burttia. Connarus. diversity microspecies polyploid

Ellipanthus, Hemandradenia and Vismianthus) and Palustria in The Netherlands and Czechoslovakia

2 Manoteae ( = Manotes), and for a small part of the (clonal diversity Hg=l— £(f| ), where f, is the

Cnestideae. Ofthe five ofthe Cnestideae of the ith clone genera only a frequency at a givenlocality).

of the of Rourea show this The were for variable minority species pattern. species analysed eight gene

Other patterns found in the Cnestideae, are the loci (6Pgdh-I, 6Pgdh-2, Mdh, Adh-2, Shdh, Lap-1 , anisocytic pattern in Agelaea, Cnestidium, and part of Lap-2 and Gpi-2). In The Netherlands, samples of T.

Rourea and the paracytic pattern in Cnestis, part of maritimum (at five localities), T. gelricum) (one

and also in Pseudoconnarus. The and T. Rourea , probably locality), hollandicum (three localities) were

stomatain Pseudoconnasus are difficult to see because examined. Mean clonal diversity per locality was

ofthe strongly papillate epidermis. In the anisocytic 0 083 + 0-146 for T. maritimum. and 0 (i.e. um-

T. pattern there are three epidermiscells surrounding the clonality) for both gelricum and T. hollandicum.

stomata of which oneis smaller than the others, these Clonal diversity for these species is low in comparison cells lack a distinct orientation. In the paracytic with other clonal plant species (average over several

of pattern on both sides the there is one studies: 0-62). Moreover, the preponderant clonal

to In maritimum epidermis cell parallel the guard cells. many pattern for T. (85% of the 298 screened

accessions of Agelaea onecan observe the helicocytic plants) was identical with the single one found in pattern and the anisocytic together in one and the T. gelricum. The single T. hollandicum clone differed sameleaf. at most loci from the T. maritimum and T. gelricum

is The fourth tribe Jollydoreae ( = Jollydora) genotypes.

T. characterized by a bicyclic pattern. In Bohemia, of 232 hollandicum individuals

The shape ofthe outer stomatal ledge varies inde- sampled at sevenlocalities all except three showed the

from pendently the pattern ofneighbouringcells but is same clonal pattern as T. hollandicum from The

within full again usually constant a genus. (A account Netherlands, The three aberrant individuals differed

stomatal features and other leaf anatomic charac- Mean on at onelocus from the typical clone. clonal diver-

1989. ters is given in Jongkind.C.C.H. Leaf epidermis sity for T. hollandicum in Bohemia was 0-018 + 0-048.

and stomatal pattern. In: F.J. Breteler (ed.): The Con- To investigate whether T. hollandicum from The naraceaea Taxonomic Study with Emphasis on Africa. Netherlands and Bohemia really represent the same

Agric. Univ. WageningenPapers 1989, 6: 21-39.) clone, small samples from both regions were screened

Vegetative characters of taxonomic value in other for 11 additional variable loci and indeed showed parts ofthe plant proved tobe available in this family uniclonality.

T. aswell, e.g. the colour and viscosity of the exudate and In contrast with maritimum, T. gelricum and several features of the such as the of T. hollandicum the T. vindobonense had wood, presence , microspecies interxylary phloem or the development of furrowed a highclonal diversity(0-897 + 0-044) at four localities branches. It is that is unable in of this regrettable one usually Slovakia. Progeny from one individual to make use of such practical characters as they are species consisted of two clones. Possible causes of the not known for all species. Collectors should pay observed amount of clonal diversity and the vari- more attention to them, report them on ability in one offspring family in T. vindobonense are MEETINGS 309

facultative agamospermy (i.e. sexual reproduction) Component Compatibility is superior to Brooks’

and autosegregation. Parsimony Analysis in historical .

other By comparing different groups with each

both methods also serve as independent tests of the Two Methods in Historical Biogeography of those phylogenies groups. Applied to the Genus Guioa(Sapindaceae)

Box P.C. van Welzen. Rijksherbarium, PO 9514,

2300 RA Leiden, The Netherlands Distribution and Speciation in Microseris

Brooks’ Parsimony Analysis (BPA; Wiley, E.O., Ann. (Compositae) Ecol. 19: and Rev. Syst. 1988, 513-542) (Component K. Bachmann. Hugo de Vries Laboratory,

M. and Roos, Compatibility CC; Zandee, M.C., University ofAmsterdam' Kruislaan 318, 1098 SM

Cladistics 3: used the 1987, 305-332) were to analyse Amsterdam,The Netherlands historical biogeography of the New Guinea species of

Guioa (Welzen, P.C. van, Leiden Bot. Ser. 1989, 12) The 16 species of Microseris (x = 9 chromosomes)

and the cicada in North America with the of genus Diceropyga (Duffels, J.P., occur western exception

Monogr. Ned. Entom. Ver. 1977, 8: 1-227). Both the allotetraploidperennialM. scapigera ofAustralia methods normally resulted in similar areagrams and New Zealand and the diploidannual M. pygmaea except for New Guinea, where BPA found a more of Chile. The species have recently been assigned

than CC did 87 and 101 three the basis of their parsimoneous areagram (resp. to monophyletic groups on

M. steps). Methodologically, the more parsimonious genomes: (1) the annual lindleyi

of areagram is always selected as the best hypothesis alone, (2) all diploid perennials, (3) all other annuals

in this the BPA geological events; case areagram. plus M. scapigera (Wallace, R.S. & Jansen R.K., Am.

the in the BPA However, geographical sequence J. Bot. 1988, 75: 214). This confirms the hypothesis results was curious, e.g. the South Moluccas together that the parents of M. scapigera are the perennial with the Solomon Islands were postulated to have M. borealis (on morphological grounds) and a North been while the in the American which has been identified onearea, geographicalsequence annual, now as

CC results was logical. Moreover, several areas and the female parentof the original hybrid. The unlikely

of in the BPA based chance groups areas analysis were on speciation by hybridization, genome dupli- the absence of species, while all groupings in the cation and successful long-distance dispersal across

CC areagram were based on the presence of species. the Pacific must have occurred and will next be studied

Due to the computer method, BPA (Wagner analysis: at the level of nuclear DNA. We are doing this already

86 with the of M. after computer programs paup and hennig ) can charac- hypothesized origin pygmaea terize areason the basis of absence ofspecies, while this chance dispersal ofa single achene from California to is impossible with the CC method (Group compati- Chile. Using a poly-GATA fingerprintprobe (Traut,

bility: computer program cafca). Methodologically it W„ Genetics 1987, 115: 493-498) we studied the

is incorrect to postulate a relationship between areas molecular phylogeny of the Chilean populations and

of of this be mutations involved in differentiation on the basis absence species, may only map species

the basis of of conclusion: from the founder individual. done on presence species. In

MEETING OF THE SOCIETY FOR PHYTOPATHOLOGY ON

11 JANUARY 1990

A of 22 lines from Effect of Genes for Partial Resistance to barley ranging extremely

susceptible to highly resistant to leaf rust were inocu- Leaf Rust in Barley on the Infection lated with leaf rust of barley (LRB), leaf rust of wheat Attempts by Inappropriate Rust Fungi (LRW) (Puccinia recondita f.sp. tritici)and leaf rust of R.E. Niks and R.G. Dekens. Department of Plant wall barley (LWB) (P. hordei murini). The proportion Breeding (IvP), AgriculturalUniversity, of early colony abortion and the size of established Wageningen,The Netherlands colonies were determined microscopically. The results

Experiments were carried out to investigate whether suggest a low (rank correlation 0-30-0-38) but signifi-

LRB genes for partial resistance of barley to leaf rust cant correlation between these parameters for

LRW LWB (Puccinia hordei)play a role in the non-host resistance (partial resistance) with those for and

ofbarley to inappropriaterust fungi. (non-host resistance). Lines with a high level of partial 310 MEETINGS

resistance to LRB were all highly resistant to LRW available which produce infectious RNA transcripts.

In and LWB. Lines with a low level ofpartial resistance this study domains ofthe 1 aprotein, aputative RNA to to LRB ranged from highly resistant relatively sus- polymerase, were exchanged between BMV and

to LRW LWB. It ceptible and is concluded that not all CCMV to locate amino-acid sequences which specify

for non-host resistance in also role genes barley play a replicationor host range determinants. in resistance to leaf rust. partial Oligonucleotide-directed mutagenesis was used to

construct an EcoRV site in the plasmid containingthe

CCMV-RNA-1 This is complete sequence. mutation

A Computer Simulation Model as a Toolto located in the middle ofthe 1 aprotein, aregioncontain-

ingamino-acid sequences which areconserved for both Develop a Testing Method for Resistance to BMV and CCMV. The mutation is translationally Whitefly ( Trialeurodes vaporariorum silent. Using this site, plasmids were constructed in Westw.) in Tomato which the 5'-half of BMV was linked to the 3'-half of W.A. Van Giessen and C. Mollema. Centre for Plant and CCMV vice versa. The respective plasmids were Breeding Research CPO, PO Box 16, 6700 AA called PBC1DV3 and PCBIDV4 (BCI & CB1). Wageningen,The Netherlands The two plasmids were used to make modified tran-

scripts of RNA-1. These transcripts were tested for The lack ofa reliable and easy-to-use testing method in-vitro their coding capability in a cell-free translation for resistance to whitefly in tomato has so far delayed Both directed of of the the release of resistant lines. system. synthesis proteins A new method was molecular Their full in leaf in which four expected mass. functioning developed using cages, whitefly par- the of the virus also tested in measured; replication was barley ameters per plant are oviposition rate

(Hordeum vulgare var. in the (OR), adult survival (AS), pre-adult survival (PS) Morex) protoplasts

presence of transcripts of RNA-2 and RNA-3, both and developmental period (DP). These parameters from BMV and CCMV (three-component system). were then fed into a computer simulation model

The two constructs were not able to supply the genetic (whitefly). This model describes the life cycle of information for the synthesis of detectable amounts of whitefly in cohorts of 1 day. The different parameters positive-sense viral RNA. dictate the speed with which this cycle is gone through Finally, their function in three-component and hence the (hypothetical) whitefly population systems was tested in Chenopodiumhybridum (local lesion host growth rate. This simulated growth rate (r ) is a s for both BMV and CCMV), barley (systemic host for measure for the level of resistance of a certain host-

BMV) and Vigna sinensis (Torner) Savi cv. Queen plant genotype. For the ultimate testing method, the Anne Blackeye (systemic host for CCMV). Neither of best suitable parameter has tobe selected, partlybased the constructs induced symptoms. on a sensitivity analysis with whitefly (and partly on In conclusion, exchanges of 5'- and 3'-halves of practical considerations). In this way it is possible to RNA-1 between two bromoviruses did not allow viral determine the relative contribution of each parameter replication in plants and protoplasts. Further tests for to the growth rate of a population. Further explo- replicability of the hybrid molecules in ration ofthe model is in heterologous progress. and homologous combinations, for synthesis of la

protein and for synthesis of minus-sense viral RNA

will be needed to elucidate the function of the la Exchanges of Domains Withinthe 1a protein and its domains. Protein From Two Bromoviruses and Their

Effect on Viral RNA Replication

B J.M. Verduin P. P.L. and 1 , Kroner, Traynor, Genetic StudiesofVirulence Inheritance of P. Ahlquist. Institute for Molecular Virology, Potato Cyst Nematodes, Globodera University ofWisconsin, 1525 Linden Drive, rostochiensis, for the Resistance Gene in Madison, WI 53706, USA, and 'present address: H1

Departmentof Virology, WageningenAgricultural Solatiumtuberosumssp. Andigena CPC

University, Binnenhaven 11,6703AW Wageningen, 1673

The Netherlands R. Janssen 1 , J. Bakker and F.J. Gommers.

Departmentof Nematology,Agricultural University, Brome mosaic virus and chlorotic (BMV) cowpea Binnenhaven 10, 6709 PD, Wageningen,The mottle virus (CCMV) are two bromoviruses: positive Netherlands, and 'present address: Research single-stranded RNA viruses with similar tripartite Institute for Plant Protection, PO Box 6700 GW, and genomes particle morphologybut different nucleo- Wageningen,The Netherlands tide sequences. They have different host ranges and

To RNA-1 ofneither BMV nor CCMV is replicatedby the estimate as precisely as possible intra-specific vari- heterologousvirus. For both viruses, cDNA clones are ations in virulence in populations of G. rostochiensis MEETINGS 311

and G. pallida.a method was developed torear cysts on development ofroot length and root fresh weight at

roots ofsprouts ofpotato in Petri dishes. Frequencies soil temperatures of 12°C and 15°C. Developmentof

ofvirulent phenotypevalues obtained with this method sprouts at 9°C was slower than that at 12°C and were more accurate than estimates on the basis 15°C during the whole period and plants reached a

of Pf/Pi-assessments determined in pot experiments. harvestable stage 1 week later.

method found tocircumvent A was the diapause of When soil cooling was used, the development of

potato cyst nematodes by avoiding desiccation of root rot decreased significantly with decreasing tem-

the cysts. Larvae were artificially hatched by cutting peratures. The negative effect ofartificial inoculation

into halves and incubation in fresh of cysts subsequent potato on weight sprouts was significantly more

root diffusate. These treatments had no influence on pronounced at a soil temperatureof 15°C.

viability and fecundity. With the artificial hatching Possible explanations for this reduction of root rot

it is five six will be discussed. procedure possible to produce to gener-

ations a year in Petri dishes and three to five

generations in pots. Virulent and avirulent lines of G. rostochiensis for Thermophilic Fungi in Mushroom Compost the H, resistance gene were selected after controlled G. Straatsma and L.J.L.D. Van Griensven.

in Petri dishes. With these lines the single matings Mushroom ExperimentalStation, PO Box 6042, inheritance of virulence determined for the was H, 5960 AA Florst, The Netherlands

resistance after the lines in Petri dishes. gene crossing Compost for cultivation ofAgaricusbisporus is almost The 3:1 segregation in avirulent and virulent larvae of completelycolonized with Scytalidium thermophilum. the Fj generation, obtained by selling the F,, showed Growth of mushroom mycelium on sterilized compost that virulence to the H, gene is controlled by a single is strongly stimulated by pre-incubatingthe compost major gene recessive to avirulence (allele A). The viru- with this thermophilic fungus. A positive relation lence percentages of the F, generations agreed with exists between the densityof S. thermophilumin exper- this finding. Reciprocalcrosses showed no evidence of imental composts and ultimate mushroom yield. sex-linked inheritance of virulence. is S. thermophilum probably already present in wheat The virulent (aa) and avirulent (AA) line were also straw (Straatsma el al. J. Gen. Microbiol. 1989, 135: used to analyse the effect of heterozygosity for viru- 751-759). lence on the development of potato cyst nematodes. Straw and agar media grown with S. thermophilum The geneticconstitution of avirulent larvae (AA and

are used as in-vitro models to elucidate essential Aa) of G. rostochiensis had no substantial influence on Growth of mushroom composting processes. rates the development into males.

mycelium on these substrates are almost ashigh as on

normal compost. The results provide further evidence

The Influence ofSoil Temperature on the for the key role of S. thermophilum in mushroom cultivation. Rate of Root Development and Root Rot in

Some additional data on wheat straw as the source Tulips Caused by Pythium spp. of S. thermophilumare presented. R.J.M. De Greeff and T.L.J. Duineveld.

Research Centre, PO Box 85, 2160 AB, Lisse,

The Netherlands Effect of the Phytotoxin of Verticillium

for Tulip commercial production are dahliaeon Several Developmental Stages of cold-treated to imitate the winter Due to this period. Tomato cold treatment the period in which the tulips develop is C. Glas, H.E. Miltenburg, B. Roy-Biswas, 60 shortened to days or less depending on the cold H.J.J. Nijkamp and J. Hille. Department ofGenetics,

treatment used. When tulips are cold-treated serious Free University, De Boelelaan 1087, 1081 HV root rot problems occur, caused by Pythium spp., Amsterdam,The Netherlands whereas under natural conditions root rot is almost

Root rot is with root negligible. coupled a decrease in Verticillium albo-atrum and V. dahliae are fungi

fresh weight and fresh weight of sprouts. pathogenicto tomato and other crop plants such as

In our experiments, different rates of root develop- potato, cucumber and strawberry. Symptoms of the

ment were attained by creating soil temperatures of disease on tomato are: wilting,browning ofthe lower

9°C, 12°C and 15°C, while the temperatureof the air leaves and in severe cases death ofthe plant. Infection

at 17°C. Gander used in these Verticillium reduction of was kept was by can cause a crop up to

experiments. 70%.

At 9°C the initial increase in root length and root Resistance against V. albo-atrum is conferred by the

fresh slower that dominant from weightwas significantly comparedto single gene Ve; V. dahliae two racesare

at 12°C and 15°C. No difference was found between known, Ve also confers resistance against race I but 312 MEETINGS

dominant resistance cultures subcultured weeks against race 2 no genes are were every 3 and I week known. before inoculation. Callus pieces (+lcm diameter)

A toxin is involved in Verticillium wilt inoculated with f. fungal were F. oxysporum sp. lycopersici.

development; this toxin can be isolated from culture race 1 or 2, usingeither drops of a conidial suspension fluid and is non-host i.e. when in of in Petri dishes specific, injected or pieces a mycelial mat grown on leaves, this toxin affects both resistant (Ve Ve) and potato dextrose agar. No differences in colonization susceptible (ve ve) plants to the same degree. The between resistant and susceptible lines were found

effect of the toxin several after inoculation ofcallus with blocks with on development stages pieces agar is investigated and a comparison is made between mycelium of race I or 2. Inoculation with a conidial the effects on tomato ( Verlicillium-resistant and suspension of race 1 ofF. f. oxysporum sp. lycopersici,

Verticillium- sensitive Lycopersicon esculentum cv. on the other hand, resulted in a different colonization

Craigella) as hosts and tobacco (Nicotiana tabacum) of resistant and susceptible callus. The growth was asnon-host for the fungus. restricted on callus derived from resistant plants,

The influence ofthe toxin was tested on the follow- whereas callus derived from susceptible plants was ing developmental levels: of ; totallyovergrown by the fungus. The accumulation of

in (detached) leaves; shoot regeneration on leaves the phytoalexin rishitin was estimated after inocu- vitro', callus leaves in shoot lation of the callus lines with F. f. growth on vitro', regene- oxysporum sp.

in ration on callus vitro; growth of minicalli and lycopersici race I and 2. Two and 3 days after inocu- protoplasts in vitro. The toxin causes necrosis on lation with race 1, significantly more rishitin accumu- leaves of both the susceptible and resistant tomato lated in the resistant line than in the susceptible

but has no effect on leaves of tobacco. line. This difference in rishitin concentration between

When isolated of in resistant and lines observed after protoplasts tomato were grown susceptible was not media containing the toxin, the percentage of surviv- inoculation with race 2. The accumulation ofrishitin ing protoplasts was affected at low concentrations in plants, after inoculation with race I, is comparable in both resistant and susceptible tomato cultivars. with the accumulation in callus (Elgersma, D M. &

Protoplasts isolated from tobacco showed a low Liem, J.I. Physiol. Mol. Plant Pathol. 1989, 34: 545-

to toxin to similar sensitivity the toxin. When the was added 555). Because ofthe results with callus cultures tomato or tobacco protoplasts after 12 days of growth and with whole plants and because of the relative without toxin, the harmful effect was much smaller. simplicity of callus cultures compared with plants,

On the developmental levels of tomato and tobacco, callus cultures of tomato provide a useful model for no significant effect was noticed. investigating the interaction between the plant and

The Verticillium is toxic F. f. phytotoxin to tomato oxysporum sp. lycopersici. leaves and protoplasts; however, on other develop- mental levels the effect is much smaller or absent.

Tobacco cells are far less sensitive to the toxin, Pyrolysis Mass Spectrometric Analysis of implying that resistance to the Verticillium toxin, in Carnation Xylem Infected with Fusanum principle, is possible. The Verticillium toxin plays an oxysporum f. sp. dianthi:Lignin importantrole in pathogenesis, it also has a clear effect Modificationsand in Diseased on tomato protoplasts but not on tobacco proto- Phytoalexins

ofthe Cultivars ‘Nevada’ and ‘Lena’ plasts; therefore it can be a potential selective agent Xylem for in-vitro selection at the cellular level for disease J.J. Boon', J. Pureveen', B. Brandt-De Boer 1 R.P. ,

2 3 resistance in tomato cells. Baayen and G. J. Niemann . 'FOM Institute for

Atomic and Molecular Physics, Kruislaan 407, 1098

2 SJ Amsterdam, Research Institutefor Plant

Protection,PO Box 9060, 6700 GW, Wageningen, Interaction Between Fusarium oxysporum and 'Willie Commelin Scholten Phytopathological f. lycopersici and Callusof Susceptible sp. Laboratory, Javalaan 20, 3742 CP Baarn, The and Resistant Tomato Lines Netherlands

B.A.M. Kroon and D.M. Elgersma. Willie Minute samples of xylem taken from healthy and Commelin Scholten Phytopathological Laboratory, f. dianthi-infected Fusarium oxysporum sp. cultivars of Javalaan 20, 3742 CP Baarn. The Netherlands

carnation were investigated by pyrolysis low voltage

Callus cultures of near isogenic lines of the tomato (15eV) mass spectrometry using a JEOL DX-303 cultivars Moneymaker and Craigella, resistant or sus- double-focussingmass spectrometer equipped with a

1 Fusarium ceptible to race or 2 of oxysporum f. sp. platinumfilament in-source pyrolysis probe. Cylindri- lycopersici were initiated. Sterile hypocotyl pieces cal samples (diameter 50 pm) with a length of about

with 1 taken from with the aid of were placed on MS medium supplemented mm larger xylem samples naphthylacetic acid and benzylarainopurine. Callus a microscope were homogenized in 20 pi of water MEETINGS 313

mini-mortar. A 5 of the method and tested using an all-glass pi aliquot Twenty plants per cross, racewere suspension was used for the PYMS analysis (mass in 10 replicates. Wilting was indexed weekly along a

20-750 1 0-5 scale 13 weeks after inoculation. range a.m.u., scan cycle s, temp gradient up to

of variance the 20°C/s up to 800°C). Analyses were performed on per-

cultivars Healthy xylem of both showed PYMS centages of diseased plants and on the numbers of spectra with markers for cellulose and hemicelluloses, plants in categories 0, 1-3, and 4-5. Method x

and a mixed guaiacyl-syringyl lignin indicated by genotype interactions were not detected, from which mass peaks indicative of monomeric and dimeric follows that root and stem inoculation resulted in the pyrolysis products. Microscopically visible infected, same relative resistance levels. Indications for extra- brown-coloured xylem of the cultivar ‘Lena’ (suscept- vascular (root) resistance were thus not found. The ible) and ‘Nevada’ (resistant) showed entirely differ- capacity to localize the pathogen at the infection site ent PYMS spectra. The PYMS of diseased ‘Lena’ appeared an important resistance component. Resist-

xylem was marked by a change in the polysacharide ant cultivars were also characterized by longer latent composition and by a very drastic change in lignin periods and lower wilting rates. These observations

to 1 pyrolysis product pattern, in which practically all apply race as well as race 2. syringyl constituents (monomeric and dimeric) were The GCA variances for resistance were highly sig-

J absent). This is evidence for a majorchange in cell wall nificant (/ <0 001) with both races. A significant

> composition and architecture due to invasion by the (/ <0 05) SCA variance was only found for resist-

2 13 fungus. ance to race at 7, but no longer at weeks after

The PYMS of infected ‘Nevada’, however, showed inoculation and could be attributed to inbreeding an overall decrease in relative intensity of the lignin depression. These data show that resistance to both

pyrolysis products but no selective changes in compo- of the races is mainly inherited in an additive way. sition. The ‘Nevada’ spectrum also showed m/z 239 This was expected for race 2 against which resistance

and 287 being molecular ions indicative of the phyto- is partial and polygenic. Resistance to race 1 had

alexins dianthalexin and methoxydianthramide S. previously not appearedpartial and was assumed to

studies be of resistance I Comparative on green xylem immediately monogenic.Additivity to race might

adjacent to the brown gum-occluded vessels showed be of the intralocus type, however, as the numbers of

comparatively low amounts of the phytoalexins, thus diseased plants were found to fitboth monogenic and

pointingto the extremely localized occurrenceof these polygenic models.

fungistatic compounds. Desorption low voltage El

3 MS of a methanol extract of about 0-2 mm ofinfected

Nevada xylem confirmed these data and showed evi-

dence for hydroxyanthranilic acid (m/z 153), diantha- Protection of Gerbera Against

lexin (m/z 239), hydroxydianthamideB (m/z 257) and Infection of Botrytis cinerea with Anti-

the methoxydianthramides B (m/z 271) and S (m/z Cutinase Monoclonal Antibodies

‘Novada’ is able 287). Evidently, to generate a strong J. Salinas. Willie Commelin Scholten,

and localized very fungistatic response to infection, PhytopathologicalLaboratory, Javalaan 20, 3742 CP

thus in its cell wall avoiding major changes Baarn, The Netherlands composition. Infection caused by Botrytis cinerea has become

in several in The an important problem crops

Netherlands. Spotting or rotting of ray florets or

Inheritance of Resistance in Carnation to gerbera flowers caused by the fungus can appear

during the growth of the flowers in the greenhouses, Races 1 and 2 ofFusarium oxysporum f. sp. but dianthi occur most frequentlyduringstorage or transport

3 ofcut flowers. R.P. Baayen12 and L.D. Sparnaaij . 'Willie

This of can be reproduced in the Commelin Scholten PhytopathologicalLaboratory, type symptom laboratory by inoculation of flowers with dry conidia Baarn, Institutefor Plant Protection, and B. cinerea. In of this case humidity is the only limiting 'Institute for Horticultural Plant Breeding,

factor. On flowers incubated at 60-70% r.h. the Wageningen,The Netherlands conidia remain ungerminated and no symptoms can

The inheritance of resistance in carnation to races I be observed. When flowers are incubated at 100% r.h.

and 2 of f. dianthi investi- the conidia short and the infec- Fusarium oxysporum sp. was produce a germtube

gated. The cultivars Novada (resistant to both races), tion occurs by direct penetration through the intact

Elsy (susceptible to race 1), Lena (susceptible to race cuticle.

2) and Sam’s Pride (susceptible to both races) were The mechanism by which pathogens breach the

selfed and intercrossed. When 3 months old, the - cuticle has been debated for almost a century.

lings were inoculated via the roots or the stems. Penetration was long thought to be mechanical, but 314 MEETINGS

the involvement of secreted the of WCS417r cutinolytic enzymes by experimentally, by a spatial separation invadingpathogens has often been postulated. and Fod by bacterization of the root and inocu-

If needed for of lation in the with microconidia of Fod. cutinolyticenzymes are penetration stem the fungus through the intact cuticle,specific inhibition Numbers of diseased carnation plants were signifi-

of cutinase activity (chemical inhibitors or mono- cantly reduced when the roots were bacterized 1

intact to stem inoculation with Fod. Pseudo- specific antibodies) can protect plants with week prior

test monas easily isolated cuticlesagainst infection. To the second possibility, sp. strain WCS417r could be monoclonal antibodies were raised against purified from the roots but never from the stem . cutinase of T ofinoculated disease control be due B. cinerea. reatment gerbera Therefore, cannot to compe- flowers with the antibodies, completely protected the tition between Fod and WCS417r. Strain WCS4l7r flowers againstthe infection of B. cinerea. is apparently able to induce resistance in carnation

to Fod. Along with induced resistance, an accumu-

lation of found in the phytoalexins was stem seg-

Induced Resistance in Carnation After ments. No such accumulation was found when

plants were bacterized only. It is concluded that Bacterization with Pseudomonas sp. Strain signals, provided by WCS417r at the root, induce WCS417r stabilization in the of defence stem responses to R. Van Peer and B. Schippers. Willie Commelin Fusarium and of the synthesis and accumulation of Scholten,Phytopathological Laboratory, State phytoalexins. Similar results on disease suppression University of Utrecht, Baarn, The Netherlands were obtained when purified lipopolysaccharides

The involvement ofother mechanisms besides compe- (LPS) of WCS417r were applied to the root instead tition for iron in the biological control of Fusarium of viable cells. Apparently, LPS of this strain is the oxysporum f. sp. dianthi (Fod) in carnation by Pseudo- inducing factor. Whether the LPS also induces monas sp. strain WCS417r, was investigated. Compe- phytoalexin accumulation is currently being tition between both micro-organisms was excluded investigated.

MEETING OF THE SECTION FOR RESEARCH ON

4 OCTOBER 1989

The Rate of Succession in Different derived from the reconstructed diameter-increment by

regression equations. Types At nutrient-poorsites such asthe Fago Quercctum, H. Koop. Research Institute for Nature generationchanges take the longest time (c. 300 Management,PO Box 46, NL-3956ZR Leersum, The years). A clear cut of 1372 triggeredaneven-aged first Netherlands tree generation. During the period 1651-1693 this tree

The rate of forest succession is most substantionally generationcollapsed and gave way to the oldest beech

influenced of the and be found Due by development tree layer. tree generation to today. to canopy

Therefore, study of growth and stature by analysis of closure of this second generation trees a regeneration

method for be in the 1693-1851. The tree rings provides a powerful estimating gap can recognized period

of the rate offorest succession. This is demonstrated in third generation trees established themselves almost

four forest associations in European forest reserves, continuously from 1851 until now.

On nutrient-rich sites such the Fraxino-Ulmetum e.g. a Fraxino-Ulmetum (He de Rhinau, France), a as

Tilio-Carpinetum (Bialowieza,Poland)and a Melico- agenerationchangefrom aneven-aged pioneer Salix-

Fagetum and a Fago-Quercetum (Fontainebleau, Alnus forest to a mixed species well structured ash-elm

The model the author forest could be recorded within 150 France). tree developed by years.

A the (Koop, H. Forest Dynamics, SILVI-STAR: compre- In Tilio-Carpinetum Picea abies trees pierced hensive Monitoring System. 1989, Springer Verlag, from an undergrowth position through a closed

for of the betulus and Heidelberg)was used depiction complex set Carpinus canopy gap replacements by of data on spatially irregularly arranged tree growth Populus tremula and Tilia cordata were found in a fine-

and stature. For the depictionofan individual tree, its grained mosaic spread in time. Here the reconstructed

dimensions such forest can be considered as within at any given time, as crown surface, dynamics cyclic a

height of the top and the crown base, have been steady state mosaic. MEETINGS 315

matter of centuries,since have Effects of Former Land Use on and many species

a limited colonization capacity. Vegetation of Woodland in very

Flanders (Belgium)

M. Hermy. Institute of Nature Conservation, The Effect ofCoppicing on Species

Kiewitdreef 3, 3500 Hasselt, and State University of Composition and Synsystematics

for Plant Gent, Laboratory Morphology, S. van der Werf. Research Institute for Nature

Systematics and Ecology, K.L.-Ledeganckstraat 35, Management,PO Box 46, NL-3956 ZR Leersum,

9000 Gent, Belgium The Netherlands

From 1977 to 1983, 640 releves were collected from In The Netherlands and adjacent countries the

183 on a variety of soils in Flanders. In relationship between high forest and coppice was

order to assess the effects of former land use on the studied in six association types ofpre-holocene soils,

and richness of the dominated and with composition woodlands, plots by Fagus sylvatica. Quercus spp. were divided in two categories: plots from ancient Betula spp. or Carpinus betulus, respectively.

recent woodlands (pre-1800) and woodlands (post- From documents and place names it was concluded

< 200 in that in and 1800; years use as woodland). under-cutting coppicing regimes Fagus-

A large number of woodland species were more or forests most probably shift gradually to Quercus-

forests and Betula-dominated forests. In less confined to ancient (e.g. Hyacinthoides non- finally to scripta, Lamium galeobdolon. Convallaria majalis. coppice, the light-indication,according to Ellenberg

Maianthemum bifolium. Oxalis acetosella) or recent (Scripta Geobotanica 1974, 9: 1-79) increases con- woodland Galium How- with nutrient of the site. Moisture (e.g. Urtica dioica, aparine). siderably poorness ever, regional differences were observed (e.g. Primula seems hardly involved, but pH and N indication are

elatior an ancient woodland species in the northern divergent; decreasing in onacidic soil,increasing , types

part, was more frequent in recent woodlands in the in types of alkaline soil. For the latter, erosion is held southern part). responsible.

is The mean number ofplant species per plot was not Although in general species composition some-

significantly different between ancient and recent what changed due to coppicing and cutting, the eco-

woodlands. However, the number of true woodland logical preferences of species from coppice do not

species was significantly larger in ancient than in deviate from those ofuncoppiced forest.

recent woodlands. Former land use did not affect the The Sorensen index for floristic composition

K. meanspecies richness per plot, but strongly influenced (Sorensen, Biol. skr. Danske Vidensk. Selsk., 1948,

the species composition and abundancy. 5:1-34) shows a mean of 68% correlation,which is of

The phytosociological classification yielded 35 the same order as variants within one association.

woodland communities from Alnion- to Quercion- With regard to ecological features, correlation is even communities. The proportion per phytocoenon in higher. Coppiced forest types can therefore be con-

plots from ancient woodland was positively correlated sidered as management variants, not deserving an

with the number of true woodland species. A positive association status.

correlation was also found with the percentages of Fagus, and other climax trees decreased in occur-

topochores and a negative correlation with percent- rence and rejuvenation, but most other trees and

ofanemochores. woodland increased in these characteristics. The ages Althoughmany com- mean

munities from recent woodlands originated before total number of species in 1208 releves increased from

1880, they still are clearly distinct from the communi- 22 0 to 24-4. Decreasing species include common

ties in ancient woodlands. In terms of woodland species and character species; increasing species

species they are not fully developed. Therefore, the include shrubs, wood-edge species of heathland or

complete renewing of woodland communities is a limestone , and nitrophilousspecies. 316 MEETINGS

MEETING OF THE SECTION FOR VEGETATION RESEARCH ON

24 JANUARY 1990

Seed After Habitat Effect of Earthworms on the Soil Vegetation Development

Bank Dynamics: An Experimental Creation in the Experimental Gardenof the

Approach RIN at Leersum, The Netherlands

K.G.A. Huijsmans and J.H. Willems. Department of G. Londo. Research Institute for Nature

Plant Ecology and Evolutionary Biology, University Management,PO Box 46. NL-3956 ZR, Leersum,

of Utrecht, Lange Nieuwstraat 106, NL 3512 PN The Netherlands

Utrecht, The Netherlands In 1972 the experimental garden ofthe Research Insti-

tute for Nature was laid out. The main Vertical movement of the seeds into the soil is a necess- Management

were to gain more knowledge about ary process in establishing a soil seed bank. The purposes

—the creation of new habitats for plant species and greaterpart of this seed bank can be found at a depth vegetation importantfor nature conservation; and of at least a few centimeters beneath the soil surface.

—the behaviour of plant species in space and time. Regeneration of plants out of the buried seeds can

The habitats were made artificially by supplying only be successful ifthe seeds are brought on or nearto

various types of soil from different areas in The the surface. From a functional point of view, vertical

Netherlands: sand poor in lime, sand rich in lime, movement of seeds in both upward and downward and others. Uniform loam, clay limestone, among direction is very important. Earthworms are supposed habitats made well i.e. factorin this were as as gradients, gradual to be an importanttransport process.

transition zonesbetween two adjacent soil types. The Experiments have been carried out to test the effect management regimes were mowing once or twice a of earthworms on vertical movement of seeds in the

dependingon the vegetationproductivity. soil. A number of cylindrical polyethelene tubes of year The developinggrasslands varied strongly in species 65-cm height and 20-cm diameter have been filled with composition and species number. This number is low calcareous soil. At two different depths ( — 2 and

in vegetationon sand in lime and nutrients and — poor 32 cm) 5-10 000 seeds of a chalk grassland species

on the formerly manured and cultivated garden soil. have been placed. All tested species have been proven

However, the on limestone and on sand to be eaten by earthworms and to survive the pass and rich in lime rich in Gradient through the intestine of these animals. In half of the clay were very species.

habitats contain than uniform habitats. number of cylinders three earthworms (Lumbricus more species

Gradients made by adding an infertile soil layer on a terrestris)were placed, resembling the worm densityin

fertile, i.e. formerly cultivated, soil were notexpressed chalk grassland.

in the actual vegetation entailing a homogeneous Six weeks after the start of the experiment the seeds highly productive grassland. The high fertility in the cylinders containing earthworms were moved suppressed variation in soil characteristics. On the vertically in both directions. This was in contrast with

contrary, the same gradientson sand in nutrients the results in the control cylinders, in which the seeds poor and lime are expressed fairly distinctly in vegetation were found in the original soil layer. with The maximum movement of seeds amounted to gradients many species. A consideration in the development of attractive approximately 10 cm, both upwards as well as

rich in flowers, is that of a downwards. grasslands, creating

varied habitat with gradientson a soil relatively poor A large number of seeds buried at a depth of 2 cm in nutrients avoiding the use offertilizers. had been transported upward and were encountered

in the worm casts on the soil surface.

There was some evidence that seeds of the several

species had been moved differently,e.g. seeds of Carex The Interaction Between Nutrient flacca tend to move upward rather than downward. Availability and the Species Composition of However, the much smaller seeds of Origanum vulgare Heathland Vegetation were found below the originalposition. This has been R. Aerts. Departmentof and recorded at both depths. Evolutionary Biology, University of Utrecht, Lange The preliminary results of the experiments men- Nieuwstraat 106, 3512 PN Utrecht, The Netherlands tioned above clearly show the effect of earthworms in

the vertical seed transport in the soil. The results will The interaction between nutrient availability and the

in be comparedwith detailed field studies order to gain species compositionof the vegetationwas studied in

Erica more insight in the role of earthworms in the mainten- Dutch wet heathland stands dominated by

ance of the species-rich chalk grassland ecosystem. tetralix and Molinia caerulea, and in dry heathland MEETINGS 317

stands dominated by Calluna vulgaris and Molinia. In the 1930s and 1940s, the vegetation structure

Biomass of dune Since the mid- production (including root production) was mainly open (dry grasslands).

2 - both about 700 whereas fifties this has been was g m year ', dominating open vegetation total of both Molinia stands was three encroached variable of productivity increasingly by patterns open times as high. In all three species total productivity low shrub. During the last 10 years the diversity in equalled litter production. Both nitrogen and phos- vegetation structures increased by the local develop-

root ment phorus loss per gram litter production (including of open low shrub into more dense and/or taller

for all due shrub the last 50 the turnover) were equal species. However, to vegetation. During years cover- the much higher litter production in Molinia stands, age of the tree layer increased proportionallyby the soil nutrient input due to litter production exceeded development of small deciduous woodlands and the that in the Erica- and Calluna- dominated stands planting ofpine forests. threefold. A great number of factors affect vegetation struc-

Competitive relationships between Erica and ture development: (meso)climate, relief, hydrology,

Molinia and between Calluna and Molinia were soil, fauna and man. In this study hydrology has been studied along an experimental gradient of nutrient of special importance. Drinking water catchment has

0 to 2 to availability, ranging from 20gNm" year" 1 . led a significant lowering of the groundwatertable

Erica Molinia when N the first half of this Later it raised outcompeted availability during century. on

2 ranged from 0 to 10 N m but lost in again as a result of changed hydrological g year 1 , compe- manage- tition with Molinia at higher levels of N availability. ment. Grazing has also been of great influence,

Calluna, however, outcompeted Molinia over the especially the termination ofcattle and sheep grazing

entire of N It is shown that the in 1920. the sudden decrease ofrabbit range availability. Moreover, graz- vertical of both deter- result of outburst in has canopy structure evergreens ing, asa a myxomatosis 1954, mines to a large extent their high competitive ability favoured the growth of woody species. with Molinia. The respect to widespread replacement Probably the present day management of ‘doing

of Calluna by Molinia in Dutch heathlands is the com- nothing’has to be changed topreventfurther loss ofthe bined result in increased levels ofnutrient availability diversity ofvegetationstructures. Maybecattle grazing

and of the Calluna heather the ofblowouts be used damage canopy, e.g. by or development can asmanage- beetle (Lochmaeasuturalis) attacks or by severe frost ment tools to retard succession and re-introduce the spells. characteristic young dune phases.

The results suggests a positive feedback between nutrient availability and dominance of Molinia in and in Dutch heathlands. Therefore, management of these Hydrology Vegetation Development heathlands should primarily be directed towards the ‘Kwade Hoek’ reduction of nutrient availability, e.g. by reduction of C. Braat and I. van Zanten'. DepartmentofNature

external inputs, or by sod-cutting, burning (in Calluna Conservation, Wageningen AgriculturalUniversity,

vegetation) or grazingby large herbivores. Ritzema Bosweg 32A, 6703 AZ Wageningen, and

'Delta Institute for HydrobiologicalResearch,

Vierstraat 28,4401 ED Yerseke, The Netherlands Halfa Century of Landscape Development

The Kwade Koek is a coastal area (350ha) situated in the Amsterdamse Waterleidingduinen west of the Haringvliet in the of the SW L.H.W.T. Geelen. Municipal Waterworks of estuary Netherlands, It is formed by growth ofthe shore since Amsterdam, Vogelenzangseweg21, 2114 BA

the late 19th century. The area consists of four Vogelenzang,The Netherlands ranges of dunes, alternated with dune valleys. The eastern

To developa scheme foradequate dune management, part is formed by saltings and mudflats, which shade

insight is required into changes in landscape, veg- off into a sandbank. The area can be inundated with

etation and hydrology. Unfortunately the Municipal seawater because it is situated outside the dike; it is

Waterworks ofAmsterdam do not have historical field bounded in the south by a seawall formed by dunes.

data concerningthe ‘Amsterdam Waterwork Dunes’. The Kwade Hoek is rich in natural gradients,caused

The question was whether changes in landscape and by sea-water inundation. Going from east towest, the

vegetation could be traced by aerial photographs. salinity of soil and groundwater, and the amounts of

Part In 1985 a pilot study started in the ‘Haasvelder- nutrients and silt, decrease. ofthe salting is being

duinen’, a part of the dune reserve, managed by the grazedby cows.

tran- Municipal Waterworks of Amsterdam. The Since the Haringvliet was closed (1970), the inun- sitions in vegetation structures were analysed by dation frequency of the Kwade Hoek has increased,

means of areal photographs from 1938, 1958, 1968, because the water level went up (30 cm). Because of

1979 and 1985. Field studies were carried out tocheck less mixture with fresh river water, the salinity ofthe

the later inundation was also increased. As of analyses. a consequence 318 MEETINGS

this the salinity of the groundwater in the Kwade To investigate whether these circumstances were

Hoek increased. This resulted in a strong spreading of representative for The Netherlands, some 35 surface the communities of the haloserie (N. Joanknecht & L. water samples were taken from different R. hederaceus

Meuleman, In: De Levende Naluur 1980,82:89-98). stands throughout the country. The samples showed

In the seawall raised. We studied wide in mineral 1977-1979, was ranges contents. Response analysis the effects of this measure on the hydrology and the showed significant correlations (P < 0 05) between the

of the and vegetation Kwade Hoek. The main results are degree of cover mineral contents of the water the following. The enlarged dune-complex caused an samples only for bicarbonate and phosphate. When increase in the amount of fresh seepage water in the the contents ofthe water were multiplied with stream southern part ofthe Kwade Hoek. This resulted in an velocity (i.e, yieldinga measure for mineral supply per increase of the groundwater level and a decrease in time unit) significant relations (FcO-05) were found the salinity in this part of the area. In the western part not only for bicarbonate and phosphate, but also for

of the area, which is not being grazed, Phragmites sulphate and nitrate. From these results it was con-

australis has partly driven out Scirpus cariciformis and cluded that the species requires a stable and high the of Mentha aquatica and Hydrocotyle supply of nutrients, while stream velocity of the water

which is vulgaris. In the eastern part, being grazed, can compensate for the lower nutrient levels found.

vegetation belonging to Galio-Koelerion and To stress the importance ofR. hederaceus as anindi-

have Loto-Trifolion and flood- cator the situation Saginion replaced species, near Oudemolen can serve mark communities (Atriplici-Cirsietum arvensis). asanexample. Previous research showed that this area

Possible for these nourished of nutrient- causes vegetation changesare: was by seepage mineral-rich,

—a change in the inundation due the R. hederaceus all pattern, to poor groundwater, was not at formation of sills elsewhere in the This area. may expected at this site, but in fact the species was found result in increase of the inundation in the an eastern there in 1971 and has increased ever since. Detailed

and decrease in the western of the part a part area; investigations showed that artificial drainage was re-

increase in the of fresh for the ofthe —an amount seepage water, sponsible diminishing deep groundwater which is beneficial to the growth ofreed; and flow, giving room for a nutrient rich lateral flow from

—the closing of the Haringvliet still has an effect on adjoiningagricultural grounds. Hence the increase of

In the vegetation development. 1977 the vegetation a rare plant species like R. hederaceus is not always

still not in environment. was equilibrium with the indicating the well-beingof a naturereserve.

Vegetation Succession and Hydrology in Ranunculus hederaceus Indicator for as an De Bollemaat, De Wieden

Changes inLand Use in The Netherlands W.J. Molenaar,R. van Diggelen and A.M.

H. Beukema, K.J. Noorman and R. van Diggelen. Kooijman1 . State University ofGroningen,

Department ofPlant Ecology, State University of Departmentof Plant Ecology, PO Box 14,9750AA

Groningen,PO Box 14,9750AA Haren, The Haren and 'State University of Utrecht, Department

Netherlands of Plant Ecology, Lange Nieuwstraat 106, 3512 PN

Utrecht, The Netherlands

In The Netherlands Ranunculus hederaceus is a rare species that occurs in flowing water, A literature sur- Vegetation succession in floating fens in relation

showed vey a large ecological tolerance ofthis species, to hydrological conditions was studied in ‘De which seems to be contradictory to its rareness, A pre- Bollemaat’,a formerpeat-digging area, situated in the

‘De liminary study correlated the distribution of the nature reserve Wieden' (NW-Overyssel, The species to groundwater systems (Diggelen, van, R. & Netherlands). An old vegetationmap revealed that in

Klooker, J. Gorteria 1990, 6: 29-38). Their results 1956 a mesotrophic and calciphilous fen community

to to seemed indicate that it was confined zones where (Scorpidio-Caricetum diandrae) was present over

of and mineral- a constant seepage relatively young large areas. A recent survey (1989) showed that only

took It seemed avoid small had remained. An of the poor groundwater place. to patches analysis veg-

with mineralized etation revealed that the seepage areas groundwater. maps calciphilousScorpidio-

R. Three hederaceus stands in the province of Caricetum diandrae was almost entirely replaced by

Drenthe (Gieten, Oudemolen and Deurze) were more acid communities (Pallavicinio-Sphagnetum selected for further investigation ofthe hydrological and Sphagnetum palustri-papillosi) or woodland characteristics. Indeed the species were restricted to (Carici elongatae-Alnetum). The Scorpidio- seepage areas where the upwelling groundwater was Caricetum diandrae was restricted to areas where characterized by a fairly low mineral content. Quality Ca-rich water was present in the root zone. Hydro-

and of the stable showed that these alkaline quantity water were very throughout logical investigations the growing . conditions were not caused by seepage of Ca-rich MEETINGS 319

groundwater. In fact the entire study area appeared more isolated sites the Ca release from the cation to be an infiltration area. The observed zonation in exchange complex is thought to be an important fac- water qualitycould best be explained by the patternof tor determining the distribution of water types and infiltrating surface water originating from the neigh- associated plant communities. bouring polder areas, where the excess of (Ca-rich) Under the present hydrological conditions the cal-

is into surface water groundwater pumpeddirectly the ciphilous Scorpidio-Caricetum diandrae represents a system. relatively short phasein the vegetationsuccession. It is

Measurements of the conductivity revealed that in- concluded that attempts to restore this community

filtration of surface water from the main water chan- should be aimed at the use of surface water instead of

nels noticeable within of 20 In the from it. was only a range m. isolating area

MEETING OF THE SECTION OF THE RELATIONSHIP BETWEEN

PLANTS AND ANIMALS ON 3 JUNE 1989

Seed Dispersal of Three Nymphaeid of N. peltata, hardly of importance in that of N. alba

and N. lutea. Within one water body hydrochory Macrophytes (Nymphaea Alba L., Nuphar seems to be the main dispersal mode of the three Lutea (L.) Sm. and Nymphoides Peltata nympaeidspecies studied. (Gmel.) O. Kuntze)

A.J.M. Smits, Laboratory ofAquatic Ecology,

Catholic University ofNijmegen,Toernooiveld, 6525 Angiospermy, Gymnospermy and ED Nijmegen, The Netherlands

The various from flower to seed release stages A.D.J. Meeuse, Hugo de Vries Laboratory, of Nymphaea alba L., (L.) Sm and University ofAmsterdam,Kruislaan 318, 1098 SM Nymphoides peltata (Gmel.) O. Kuntze have been Amsterdam,The Netherlands described by Van der Velde and Van der Heijden

Bot. 10: and Van der Velde differ from in that the (Aquat. 1980, 261-294) Angiosperms

(Acta Bot. Neerl. 1986, 35: 111-113). However, infor- endostome (orifice of the integument)is not exposed,

mation concerning the dispersal of the diaspores of which means that the role of the pollinationdropletas

these plants was scarce and incomplete. Recently, apollen-receiving device was replaced in angiosperms

several aspects of the hydrochorous, endozoochorous by the stigmatic surface. As the droplet was also

and epizoochorous dispersal of these nymphaeid involved in early entomophily, the insect visitors had

examined. These be lured in other if biotic had macrophytes were were: (1) to some way pollination

maintained. buoyancy of seeds or carpels; (2) survival of seeds to be Several escape routes were possible,

after the passage through digestive system of two but the change-overto angiospermycannot have been

and fish aquatic birds one species; and (3) desiccation an abrupt happening (otherwise the reproduction

tolerance ofthe seeds. would not have been continuous). Conceivably, an

of N. lutea found be intermediate have in Buoyancy carpels was to poor phase may existed, especially

N. comparedto alba and in particularN. peltata seeds. cases where alternatives (nectaries, deceit, pollen as

Mallard duck (Anas platyrhynchos L.) and coot reward) did not develop. What onewould expect is an

N. N. those (Fulica atra L.) digested all seeds of alba, lutea exudate from the tip ofthe carpel or style in cases

and N. peltata completely, in contrast to seeds of where the stylar canal is not closed at anthesis. This

Potamogetonnatans L., P. obtusifolius Mert. et Koch condition is found in Nelumbo and apparentlyin some

and P. pectinatus L. Similar results were obtained species of Drimys; the exuded droplet is consumed by

when the seeds were fed to common carp (Cyprinus and pollen is absorbed by it. In Nelumbo

carpio L,). Because of the complete digestion of the the stylar canal is incompletely closed by hairs at its

seeds ofthe duck and distal that that the of nymphaeidwaterplants by coot, end, so onemay speculate origin

carp,endozoochory will not contribute to a successful the sticky stigmatic fluid and the papillae in angio-

have from transitional dispersal. sperms may originated a

Unlike N. the seeds of N. alba and condition still found in the Nelumbo. peltata seeds, primitive genus

N. In lutea were killed by desiccation. view of these Researchers are advised tolook for exuded droplets

properties and the morphology of the seeds it can be on carpel tips in primitive families and in taxa where

concluded that be fac- there is connection between and epizoochory may an important a apex

tor in the between isolated water bodies through tegumentary protrusions. 320 MEETINGS

Flower Choice by Bumblebees: Cause and Preference for Melampyrum flowers can be explained by the higher content of Melampyrum Consequences for the Plant (40%; Viscaria 25%) and the possibility of M.M. Kwak and O. Jennersten 1 . Laboratory ofPlant collecting both pollen and nectar from the same Ecology, Biological Centre, PO Box 14, 9700 AA of flower. Energy intake per minute, a combination Haren, The Netherlands and ' Department of volume, concentration and visitation speed was Zoology, Uppsala University, Box 561, S-751 22 more profitable in Viscaria. Nectar composition did Uppsala, Sweden not offer an explanation for the preference for

Bumblebees foraging on two sympatrically, simul- Melampyrum. taneously species, Melampyrum Seed production in Viscaria was affected, especially

and Viscaria late in the the switch of bumblebees from pratense (Scrophulariaceae) vulgaris season, by

(Caryophyllaceae) were studied during the flowering Viscaria to Melampyrum, resulting in a low visitation season of Viscaria in Sweden. Both species shared and the change ofimproper pollen transfer. the main of Bombus which Seed in was also lower visitor, queens hortorum, production Melampyrum

nectar collected on both species but pollenparticularly later in the seasonbut this was mainlya result ofpolli-

nator on Melampyrum. The pattern of visitation changed satiation because Melampyrum became very over the season; bumblebees preferred Viscaria early abundant with lime. but changed to Melampyrum later in the season Although Viscaria flowers produced large amounts

(1986); in 1988 they preferred Melampyrum from the of nectar (4 pi per flower) especially later in the season, beginning onwards, but early Viscaria flowers still other bumblebee species did not start to visit Viscaria. received about 5-5 visits flower per per day.