IAWA Bulletin n.s., Vol. I (1-2), 1980 49

ON THE STEM ANATOMY OF CLEMATIS VITALBA L.

by

Markus Sieber and Ladislav J. Kucera Institut fUr Mikrotechnologische Holzforschung der ETH, 8092 Zurich, Switzerland

Summary Results and Discussion The present study deals with the stem anat­ The pith of Old Man's Beard is composed omy of Clematis vitalba L. as observed by light solely of parenchyma cells. The presence of a microscope and SEM. Special attention is given cavity (Figs. I, 5, 8, 15) in the centre of the to the pith, the fascicular and interfascicular pith is very characteristic. This cavity is restrict­ cambium and the water-conducting system. ed to the internodes, in the region of the nodes Some inconsistent data in literature are discus­ a diaphragm was always found. In the first sed. comprehensive study on the pith structure in woody plants Gris (1872) described different Introduction kinds of pith including a heterogeneous type Old Man's Beard (Clematis vitalba L.) is one composed of a continuous cavity within the of the few woody climbers of the forests of internodes and solid membranes in the nodal Europe and the Middle East. The cosmopolitan zones. He included Clematis flammula in this genus Clematis belongs to the Ranunculaceae type. Gris emphasized the solid character of and includes about 300 species (Melchior, the cells in the diaphragm as opposed to the 1964). Like many other lianas Clematis vitalba 'spongy and light' cells in the rest of the pith. is characterized by two main features: the ex­ Kobler (1908) who measured the diameters of traordinary water conducting capacity of the the stem pith of several plants did not mention vascular system, and the flexibility of the stem. a pith cavity in Clematis vitalba. Kassner ( 1884) In addition to giving a general description of did research on different stages of the forma­ the anatomical structure of the stem the aim of tion of the pith cavity in Ribes. Ampelopsis. the present study is to clarify some hitherto de­ Evonymus. Lycium. Pterocarya and Lonicera. batable points. He concluded from his observations that the reason for the formation of a pith cavity was Materials and Methods the fact that the innermost pith parenchyma Specimens were collected from healthy adult cells have non-lignified walls and therefore dis­ plants growing in several typical habitats in integrated. This statement was confirmed for Switzerland. Light microscope observations Clematis vitalba in this project, where the in­ were made on safranin/fast green double-stained nermost non-lignified pith cells (Fig. 4) could microtome sections of 15 Mm thickness. Draw­ be distinguished from the lignified cells with ings of several transverse sections were made thick multilayered -walls (Fig. 7) with the help with the help of a projection microscope, and of a double stain. The formation of a pith cavi­ the percentage area of different tissues was de­ ty is certainly a secondary process during termined gravimetrically. The height of rays which the walls of the central pith cells are de­ was determined using the 'surface photography composed (possibly enzymatically), beginning method' after Zimmermann and Tomlinson from the center outwards (Figs. 3,4). This pro­ (1967). Of three specimens, each including two cess does not necessarily occur in each interno­ nodes and one internode, sequential transverse dium or each individual plant. We observed surfaces 0.1-0.5 mm apart were photographed several stems of different ages with a continu­ with a movie camera. For contrasting the sur­ ously solid pith. faces a successive treatment with a 2 % aqueous The stem of Clematis vitalba is a dicotyle­ phloroglucinol solution and 25 % hydrochloric donous vine type with 6 big and 6 small vascu­ acid proved to be the most satisfactory. Orien­ lar bundles in its primary state (Figs. 3, 5). The tated wood blocks for observations in the scan­ vascular cambium consists of fusiform and ray ning electron microscope (SEM) were prepared initials in the fascicular region, and of ray ini­ following recommendations by Exley et al. tials only in the interfascicular zone. The young (1974). secondary stem thus shows a pattern in trans-

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Downloaded from Brill.com09/27/2021 02:08:05PM via free access IAWABulletinn.s., Vo!.1 (1-2), 1980 51 verse section of 12 islands consisting of vessels, the stem into sectors enables it to withstand axial parenchyma cells, fibres and narrow sec­ the resulting twisting forces like an elastic la­ ondary rays, the islands being separated by 12 mellar structure. broad primary rays. The cambium is more ac­ The anatomical structure of the secondary tive in the fascicular than in the interfascicular xylem has been described by many authors region and again more active in those fascicular (Dadswell and Record, 1936; Record, 1936; zones which derive from big vascular bundles Schmidt, 1941; Metcalfe and Chalk, 1950; than those deriving from small ones (Figs. I, 2). Greguss, 1959; Grosser, 1977; Schweingruber, The result is a cogwheel-like appearance of the 1978), but there still are some points to be stem in transverse section. In addition the cam­ clarified. The cambium of Old Man's Beard be­ bium is dented towards the pith in the region comes active before bud break which is typical of the broad rays (Fig. 2). The difference in the for ring-porous woody plants (Ladefoged, structure between fascicular and interfascicular 1952). The annual rings are narrow and indis­ cambium is persistent. It can be observed dur­ tinct (Fig. IS), except in fast-growing indivi­ ing many years of the further radial growth, duals. Axial elements (vessel elements and axial and also throughout an entire internode. This parenchyma strands) are stratified (Figs. 12, feature seems to be typical for lianas and some 16). To our knowledge the percentage area of bushes. Balfour (1958) found the same situa­ the different tissues has never been determined tion in Macropiper excelsum Forst. of the Piper­ in the secondary xylem of Clematis vitalba. aceae. The same is true for some species of Our measurements produced the following dis­ Casuarina as well as Dutchman's Pipe (Aristo­ tribution: lochia sipho; Philipson et al., 1971; Troll, 1973). Rays 12.8 + 5.6 % In view of this persistent difference and the in­ Ground tissue (axial paren­ distinct structure of the meristem in the inter­ chyma + fibres) 22.2 + 13.3 % fascicular region, doubts have arisen whether Vessels 65.0+ 17.2 % the cambium is not restricted entirely to the fascicular region, i.e. whether the meristem in In their comprehensive study on numerous the interfascicular region can be regarded as indigenous Central European and foreign hard­ cambium according to its generally accepted woods Huber and Priitz (1938) mention maxi­ definition (Philipson & Studholme, 1966). The mum values of 50.7 % for the vessels in root physiological importance of the rigid division wood of elm (Ulmus effusa Willd.) and only of the stem into fascicular and interfascicular 39.5 %in the stem wood of narrow-ringed oak sectors has been discussed by Philipson et al. (Quercus pedunculata Ehrh.). The high percen­ (1971). Based on the opinion expressed in the tage of vessels in Clematis together with a high aforesaid book the following explanation ap­ transport velocity (Huber, 1956) explains the pears to be probable: The stem of a liana is not extraordinary water-conducting capacity of the self-sustained, but needs support. It is fixed to vascular system. a host plant at several points which are distant The early wood vessels are circular in trans­ from each other. Inner and outer forces such as verse section and have a diameter between 100 gravity, wind, snow etc. result in considerable and 300 /lm. They are usually arranged in one, changes of position of the stem. The division of occasionally two, tangential rows. The late

Fig. 1-8. Clematis vitalba L. -- I: Transverse section of a young stem. The dark stained peripheral zones of the xylem indicate the actively conducting tissues; x 4. -- 2: In transverse section the tis­ sues of the bark form arcs outside the fascicular regions. In the interfascicular zones wedge-shaped indentations can be observed (sclerotic portions of rays). Photomicrograph, TS; x 32. -- 3: Trans­ verse section of a young stem. Notice the size and arrangement of the vascular bundles and the ab­ sence of a cavity in the pith. Photomicrograph, TS; x 32. -- 4: Detail from Fig. 3. The presence of 10 thin-walled cells with large intercellular spaces indicates the beginning of the formation of a cavi­ ty. Photomicrograph, TS; x 210. -- 5: Transverse section of a one-year-old stem. Notice the 6 big and the 6 small vascular bundles and the pith cavity. SEM photograph, TS; x 22. -- 6: Seen in transverse section the secondary xylem is ring porous. The vascular strands are separated from each other by broad rays. SEM photograph, TS; x 50. -- 7: The thick-walled cells of the pith are sclero­ tic and their walls are multilayered. SEM photograph, TS; x 2700. -- 8: In the internodes of older stems we usually find a pith cavity with a smooth surface. Cells bordering the cavity are extremely thin-walled. SEM photograph, TS; x 275.

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Downloaded from Brill.com09/27/2021 02:08:05PM via free access IAWA Bulletin n.s., Vol. I (1-2), 1980 53 wood vessels are 30-50 j.l.m in diameter. They They have thick, lignified walls with simple are often arranged in tangential or radial multi­ pits. Spiral structures between the primary and ples (Figs. 2, 6, 14, IS). The vessel perforations secondary wall as described by Greguss (1959) are simple, and the perforation plates are hori­ could not be observed. It is, however, possible zontal in the early wood vessels, but rather ra­ that Greguss mistook the very narrow spirally dially oblique in the late wood vessels. Intervas­ thickened late wood vessels for fibres. Starch cular pitting is alternate. Without exception the granules were present in many fibres, indicating late wood vessels exhibit helical thickenings that in addition to axial and ray parenchyma (Figs. 9, 10). Tyloses are absent, but deposits the fibres are partly responsible for storage. of gum-like substances may be present in some One of the reasons may be the very small quan­ vessels. The mechanisms of the occlusion of tity of axial parenchyma. Wolkinger (1969) de­ vessels remains obscure. An experiment with scribes the occurrence of living and partly vital staining (Fig. I) showed that vessels cease starch-storing fibres in several woody plants in­ to function in Clematis vitalba after 2-3 years. cluding Clematis. Thus there must be some form of occlusion. The biggest discrepancies in literature are The formation of heartwood as described by found in connection with the description of Schmidt (1941) could not be observed clearly. the rays. In standard literature De Bary (1877) However, black-stained zones could be seen, and Huber (1961) mention that in certain plants starting from the primary xylem of the 6 big the primary rays may have the height of an en­ vascular bundles (Fig. 14) and spreading out­ tire internode, and both include Clematis in wards (Fig. 13). The function of this black this group. In specialized wood anatomical lit­ stain is not clear. Grosser (1977) suggests a erature (Schmidt, 1941; Metcalfe and Chalk, fungal infection, but in view of the place of 1950; Greguss, 1959; Grosser, 1977; Schwein­ origin this does not seem very probable. Fur­ gruber, 1978) heights of 2-3 em are given for ther research is necessary to find an explana­ the rays in the secondary xylem of Clematis. tion as well as a possible connection with the The authors of this study consider it crucial to formation of heartwood and the occlusion of distinguish between primary and secondary vessels. Due to the high amount of wide vessels, rays, which might explain the above-mentioned carbonized wood of Clematis could be used differences. The primary rays usually have a successfully as a matrix for bone-regeneration width of up to 12 (occasionally 20) cells and in mice and rabbits (Colville et aI., 1979). originally the height of an entire internode. The axial parenchyma is scarce, which may During secondary growth their height is reduc­ be the reason for the discrepancies between ed through intrusion of fibres, possibly also different descriptions. Greguss (1959) and vessels and axial parenchyma cells. The second­ Grosser (1977) describe its arrangement as apo­ ary rays are distinctly narrower and shorter tracheal, whereas Schmidt (1941), Metcalfe (about 1/3 of the height of an internode). The and Chalk (1950) and Schweingruber (1978) rays are heterogeneous (Fig. II) and belong to consider it to be paratracheal. In fact there is type III according to Kribs' classification para tracheal vasicentric as well as apotracheal (Kribs, 1935). Sheath cells occur occasionally. parenchyma. One parenchyma strand consists of 2, occasionally 3, parenchyma cells with rel­ References atively thick, lignified walls and simple pits Balfour, E.E. 1958. The development of the (Fig. 12). vascular systems of Macropiper excelsum The fibres are non-septate and of the same Forest. II. The mature stem. Phytomorph. length as the vessel elements or slightly longer. 8: 224-233.

Fig. 9-16. Clematis vitalba L. -- 9: Detail of a vascular strand. Notice the narrow late wood ves­ sels with spiral thickenings. SEM photograph, TS; x 580. -- 10: Late wood vessels with alternate bordered pits and spiral thickenings as seen in radial longitudinal section. SEM photograph, RLS; x 1050. -- II: Upright, square and procumbent ray parenchyma cells. SEM photograph, RLS; x 340. -- 12: Fibres, parenchyma strands and late wood vessels as seen in tangential longitudinal section. Notice stratified arrangement. SEM photograph, TLS; x 240. -- 13: Transverse section of a very old stem with conspicuous black stained central portion; x 0.6. -- 14: Two big vascular strands with black stain and a small one without stain in the centre of the stem. Photomicrograph, TS; x 32. -- 15: Transverse section of a stem of an adult plant. Notice the pith cavity and the tis­ sue arrangement in the secondary xylem. SEM photograph, TS; x 26. -- 16: Axial elements are stratified. Photomicrograph, TLS; x 120.

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