VES FISHERIES RESEARCH BOARD OF CANADA NacW Translation Séries No. 2664
Diatomaceae (siliceous algae)
by Friedrich Hustedt
Original title: Kieselalgen (Diatomeen)
From: Sammlung: Einführung Kleinlebèwelt' (SerieS:; . Introduction tb the world.ofjnicrci-organisms), 1-7(),. 1965
Translated by the Translation Bureau(ËS) Multilingual Services Division' Department of the Secretary of State of Canada
Department of the Environment Fisheries Research Board of Canada Great Lakes Biolimnology Laboratory Burlington, Ont. 1973
114 pages typescript DIATOMACEAE
(SILICEOUS ALGAE)
FRIEDRICH HUSTEDT ^ 1 ^ --). ^1^Z/ ^. DEPARTMENT OF THE SECRETARY OF STATE %.^^ SECRÉTARIAT D'ÉTAT
TRANSLATION BUREAU (?'r . N) BUREAU DES TRADUCTIONS t,, A. MULTILINGUAL SERVICES f:..<<: ^f DIVISION DES SERVICES CANADA DIVISION _ MULTILINGUES
TRANSLATED FROM - TRADUCTION DE INTO - EN German English
AUTHOR - AUTEUR Friedrich Hustedt
TITLE IN ENGLISH - TITRE ANGLAIS Diatomaceae (siliceous algae)
TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) TITRE EN LANGUE ETRANGERE (TRANSCRIRE EN CARACTÉRES ROMAINS) Kieselalgen (Diatomeen)
REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE FOREIGN CHARACTERS. REFÉRENCE EN LANGUE ETRANGÉRE (NOM DU LIVRE OU PUBLICATION), AU COMPLET., TRANSCRIRE EN CARACTÉRES ROMAINS.
Sammlung: EinfUhrung in die Kleinlebewelt
REFERENCE IN ENGLISH - REFERENCE EN ANGLAIS Series: Introduction to the world of micr6-organisms
PAGE NUMBERS IN ORIGINAL °UBLISHER - EDITEUR DATE OF PUBLICATION NUMEROS DES PAGES DANS Kosmos Gesellschaft der Naturfreunde DATE DE PUBLICATION L'ORIGINAL Franckh'sche Veriagsbuchhandlung 70 YEAR ISSUE ,NO. VOLUME PLACE OF PUBLICATION ANNÉE NUMÉRO NUMBER OF TYPED PAGES LIEU DE PUBLICATION NOMBRE DE PAGES DACTYLOGRAPHIEES Stuttgart (Germany) 1965 114
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GGIÈNrt'S N0. UEPARTMENT 01 KISI ON/ BRANCN NO [1U GLIENT N4INISTERE nIRISION3 QIRECTION
Eia.vironn^ent ^^c . 51.ip. viv., Lib.., i r.l. I"I zl.d Waters t3URE`kU NO. . IIANGUA G E TRANSLA•TOR 1 I NI T1 A LS ) I^0'[SU OUREAU LANGUE TRADUCTEUR ' (INlT1ALES)
Ge:rnan
Reference: F:iustedt, Friedrich; KieselaÎgen (Diatomeen). Stuttgart: FrancTd:i'sche Verlagshandlung W. Keller & Go., 3rd edition 1965.
Diatomaceae (siliceous algae)
Dr. Friedrich Hustedt Bremen (Germany)
With 35 drawings throughout text and 97 illustrations on 4 Plates
(Contents Page No. 0 @rig. Transl. Odhat are "'s^t liceou^s a Igae'Y? ...... 7 2 General structure of the diatom cell ...... 8 4 Structure of the cell wall ...... 13 15 Raphe and motility ...... 19 25 GeTl contents ...... 2.3 34 Formation of colonies ...... 24 36 Reproduction ...... 27 41 Variability ...... 33 52 Liâcology ...... 34 54 a) Hydrogen-ion concentration ...... 34 55 b) Calcium content ...... 35 57 c) Salinity ...... 36 58 d) Nitrogen and phosphorus ...... 36 60 e) Other chemical factors ...... 37 61 f) Water current ...... 37 61 g) TemperRture ...... 37 62 w h) Light ...... 39 65Z Ln ^'lotation aids ...... 39 65h Nutrition and 67 <1 ^ ^ F- prLp^>.ration of cultures, ...... 40 ^ Collection of material ...... 42 70cn c :x ^ 727 ° O cu Inspection ...... 43 - Preparation of raw material ...... 44 74cs ` ^ 0 Mounting and conservation ...... 45 78 Drawings and photographs ...... 47 81 0 1^ 4 (a The importance of the Diatomaceae...... • 48 83^' Tables for determining familles and genera ...... 49 84 References ...... 62 Inc: ;^: ^ Legends of plates :i-IV ...... 64 108 ^-- Index ...... 69
aOS-zoo-I O'31 2.
What are "siliceous algae" ? p. 7
The answer to this question lies already in its formulation. They
simply are algae with silicified cell walls. For about one and a half
century many investigators and lovers of nature have devoted themselves
to the study of these unique organisms which were regarded by some to be
of animal and by others to be of vegetable nature. These early investiga-
tors were first intrigued by the multitude of such organisms in our waters
and the capacity of independent movement, unknown in the vegetable kingdom,
but observed_in some species; later, with the perfection of the microscope,
they were fascinated by the structure of the cell walls which reveals the
artistry and creative power of Nature in extraordinary abundanceand by which alone the living plasma is rendered viable. Soon enough,the com-
plete rigidity of these cells in contrast to other plant cells,,=and their
resistance to chemical reagent's was observed and it.was realized that the
cell wall consists of a siliceous membrane embellished by multifaceted
"adornments." On account of these siliceous walls, they were called "si-
liceous infusoria," "siliceous Bacillaria," and,._finally, "siliceous al-
gae." In contrast to this characteristic- German designation, the custom- ary scientific terms "Bacillariophyceae" and "Diatomaceae" give no clue as to their nature. The name"Baciliariophyceaé1 relates to the rod-shaped frustules of the first-known genus Bacillaria, while the most widely-used
terml'Diatomaceae"has been derived from the genus Diatoma and is indicative merely of reproduction by cell division,which is known, however, to be
the most common process in the world of organisms.
The silicification of the cell walls led to a wealth of differen-
tilations from other organisms to assure viability and reproductivity; hence, 3.
the Diatomaceae form a rather isolated group within the vegetable king-
dom although, here and there, a faint resemblance^reminiscent ofa clo- 0 ser relationship,exists.They belong to the microscopic unicellular orga- nisms which play a prominent role in the economy of our oceans and in-
land waters. In numerous sediments their nearly indestructible valves
bear witness (in some cases after millions of years) to growth and decay
on our planet, the elevation and submergence of its land masses, and
the eternal battle between the sea and the land. The most minute frust-
ules measure 0.0025 mm, while the largest discoid valves measure close
to 2 mm,and rod-shaped species may surpass the length of 2 mm; however,
such "giants" are rare exceptions.
The environment of all Diatomaceae is the water, whereby, for some
species, the most minute amounts of moisture.will .suffice. Damp.mo.ss
patches-on tree trunks, glass panes in greenhouses, the atmospheric moist-
ure settling on mountain walls, and the damp soil,all accommodate more or
less dense colonies of aerobic ("air-loving") diatoms, frequently of ex-
tremely delicate structure. In our waters they populate not only the open
water as floating plantswith the help of special processes, but cover also
the bottom as far as light can effectively penetrate, and all substrates
along the shore zone such as higher plants, wood and rocks. There, usu-
•-ally-fiogether with other algae, they.frequently form a thick brownish car-
pet in which numerous minute animalcules find food and shelter. Some spe-
cies,especially of the genus Nitzschiaaoccupy even highly polluted waters
where they provide,together with bacteria and several other organisms,the
preliminary conditions essential for the biological self-purification of
these waters. 4.
Industry also has taken hold of the diatoms and produces dynamite, insulating material for heating systems, and filters from the fossil depo- sits known as diatomaceous earth or diatomite.* Emperor Justinian* alleged- ly used,as early as 526 A.D., the "light, floating bricks" -- again diatoma- ceous earth -- in the construction of the St.Sophia cathedral*.
General structure of the diatom cell
In the literature, the diatom cell is usually called "frustule"
(from the Latin frustulum = small piece), or, even better, "theca" (Greek word, meaning box, capsule) since it is indeed constructed like a pillbox of two main parts, namely the lower bottom * part or "hypotheca" and the overlapping cover or "epitheca" (Fig. la). But just as the two halves of a pillbox usually again consist of two separate parts, namely bottom and top each with its connective part, so also are the epi- and hypotheca of the diatom frustule each composed of two distinct parts. Cover and bottom are called shells or valves, the connection is formed by the two zones capable of movement over each other and known also as pleurae. However, in most cases the edges of the valves are more or less inverted and par- ticipate,thus,in forming the suture. This portion of the valve,which is very conspicuously developed, for example,in the genus Meloseira,is known as the connective zone. Thus, the mature frustule of a vegetative diatom
*) Translator's notes: Diatomite serves to filter and clarify many liquids. It is -an excellent insulating material for boilers, blast furnaces and refrigerators. It is used also as a mild abrasive in metal polishes, scouring powders and tooth pastes. (M.H.Berry: The Algae; The Book of Popular Science, 4:294 (1958), New York - Toronto, The Grolier Society Inc. Justinian I. (Flavius Anicius Justinianus) A.D. 483-565, Roman emperor. Properly: Hagia_Sophia, a -church in Istanbul (Constantinople) re- garded as one of the wonders of the world. Jus tian entrusted its design and construction to two distinguished architects, Anthemius of Tralles and isidorus of Miletus. 5. E consists at least of the following parts (Fig. la): Cover (upper or epi- valve), upper (= outer) connective zone (epipleura); lower (= inner) con-
nective zone (hypopleura), bottom (lower or hypovalve). These parts are
not inextricably intergrown with one anothErbut can easily be detached me- Il chanically; this fact is of decisive importance for the frustule's viabili- 0 ty and for reproduction. Since the two bands that form the suture are not immovably united, it follows that the two parts of the frustule, namely
epi- and hypovalve, are capable of movement over one another just like the
two parts of a pillbox. For this very reason, the guideway controlling this
direction of motion and, hence, connecting the morphological centers of both 0 valves, is called "pervalvar axis" (Fig. lb). Of course, it runs also through the morphological center of the frustule constituting at the same time its
longitudinal axis,although, in most cases, it does.not represent the longest
extent of the frustule. Axes intersecting the center of the pervalvar axis
at right angles are called "transverssl axes;" the plane determined by them
is the central cross-section of the frustule. If the latter is circular,
the transverse axes are alike and may,thereforetsimply be.considered as the
diameter of the frustule. However, if the cross-section is more extensive
in one direction, that is, if the valves have an elliptical to linear shape,
Fig.l: Basic structure. P a = apical view; b=.axes and planes. V= valves, P = connective zones, ,r E epivalve, H = hypovalve, A-B = per- F valvar axis, C-D = apical axis,E-F = r o o transapical axis, G-K = parapical axis, L-T1 = paratransapical axis, C-E-D-F = b valvar plane, G-H-J-K = apical plane, L-M-N-O = transapical plane. 6.
the two main axes of the cross section each require a snecific designa- tion since orientation throughout the frustule would otherwise be impos- sible. The longer of the transverse axes is,therefore,designated as api- cal axis, and accordingly, the shorter one as transapical axis. These lines determine the principal planes of the frustule, they are essential systematic factors; an intelligent comprehension of the microscopic pic- p.9 ture would be inconceivable without them. The-aforementioned central cross-section determined by the transverse axes, that is, the apical and the transapical axes, represents the valvar plane, so designated because
it runs parallel with the valves and, hencé, duplicates in most cases the
form of the latter. The plane determined by the pervalvar and apical axes
is called apical plane, that determined by the pervalvar and transapical
axes is termed transapical plane. All axes mentioned.relate.always to the
cell body; hence, their course runs through the frustule. However, in
some instances, it it necessary to name also the corresponding axes of
the valves; however, the misleading terms "longitudinal" and "lateral"
axes are to be avoided since the longitudinal axis of the frustule is not
identical with that of the valves. In fact, the latter runs parallel
with the apical axis and is,therefore,called parapical axis, while the
lateral axis of the valve, running parallel with the transapical axis,
is designated as paratransapical axis. Besides the nomenclature here
applied and-originally introduced by Otto MULLER, other terms have been
suggested,but these are, -on purpose, not mentioned here since the appli-
cation of different terminologies for one and the same topic can only
lead to confusion. MÜLLER's terminology, once thought through and tried
out in practice, is most simple and clear without ver leading to mis-
7.
Ufidêrctândings. The main sections do not necessarily-have to.be always
absolutely straight; depending upon the shape of the frustule, they may.
frequently be arched or bent in one or both directions, often S-shaped,
and not seldom also spiraling around one of the axes. Furthermore, both along the frustule,when separated , one of the principal sections, halves of /‘ may be either similar or different. In the case of similarity, their corn-
on axis shows isopolarity, in the opposite case heteropolarity (Fig. 2).
Here again, it must be kept in mind that axial polarity always relates to
the cell body, and that structural differences of otherwise similar valves
are not taken into account; in doubtful cases, both aspects of the frus- tule should be inspected, namely the valve view as well as the zone view (if seen in zone view, frustules, split open on one end,may simulate hete-
ropolarity!). As we .have seen, the epivalve overlaps the hypovalve and
IS therefore always larger, in thick-walled species even considerably so.
nence, the pervalvar axis would, strictly speaking, always represent he-
teropolarity and there would be no way to distinguish between the spe-
cies which,.according to their form, show true heteropolarity) and all the
rest. FOr this reason, if it is only a question of difference between
the sizes of epi- and hypovalves, we accept the pervalvar axis as being
isopolar '(but not if such differences involve the poles of the two re-
maining axes!).
Fig.2: Polarity of the axes. a I . (isopolarity), c 2 pervalvar axis (heteropolarity); el (isopolarity), axis (heteropolarity); .... h (isoporarity), apical axi (heteropolarity). LJ
8.
the As for Asimilarity of the cell halves on either side of the princi-
pal section, Otto MULLER distinguished complete similarity from resem-
blance, symmetry from consimilarity. This differentiation is, in my opin-
ion, unnecessary; we can dispense with emphasizing consimilarity because,
here again, it is merely a matter of difference in the sizes of the two
valves, which is of no practical importance for the understanding of the
frustule's morphology. On the other hand, in agreement with MÜLLER, I dis- p•10 0 tinguish the following four types of symmetry which are of . decisive impor- tance also in systematics:
0 1. Mirror-image symmetry (one,Yalve of the frustule being the
mirror image of the other);
2. Diagonal symmetry (oneVâlve of the frustule being turned ri against the other by 1800); 3. Antisymmetry (the mirror image of one Valve of the frustule
0 being turned against the other by 1800);
4. Asymmetry.
Fig_3: Mirror-image symmetry. Eunotia djdyma; valvar form and po- ]sition of raphe in b (hypovalve) re- ^present the mirror image of a(epi- 0 ;valve).
. Fig.4: Diagonal symmetry. Pinnularia flamma; the course of the raphe on one valve is the opposite"of that on the other.
Fil 9. 0 MÜLLER's theories are not in all cases easily applicable to actual conditions in the Diatomaceae. Therefore, a practical method is offered 0 here which makes it easy to understand the conditions of symmetry. For each of the first three examples we need a piece of white carton (approxi-
mately postcard size) and a piece of tracing paper; the sides of the car- I ton are to be numbered 1 and 2, the sides of the tracing paper 3 and 4. Examplé l(Fig.3, p.8): An entire frustule of the largest avail- 0 able species of the genus Eunotia (valve view) is selected as the object. With the help of.a drawing pen, a sketch is made on side 1 of the carton
0 illustrating the valve as it represents itself to the observer, that is, 0 its outline and branching of the raphe only. In the same manner, a sketch of the other valve of the frustule is made on side 3 of the tracing paper. 0 However, since this second valve is seen from its inside, the sketch is traced with India ink onto side 4; both pieces (sides 2 and 3) are then 0 pasted together in such a fashion that the sketches perfectly match. If 0 side 1 of the drawing is now held up against a plane mirror, its image will be identical with the sketch on side 4; hence, the two cell halves
show mirror-image symmetry.
Example 2 (Fig.4, p.8): A large Pinnularia species whose terminal
0 fissures on either side take opposite directions serves as the object.
Following the same procedure as described for example 1, we find upon e viewing the image in the mirror that it does not correspond to the out-
lines on side 4; to achieve this, the drawing held against the mirror
must be turned by 1800 about its parapical axis, and hence, the two the valves are subject to diagonal symmetry (apparently, turning,mirror and,
N 10.
thus, the imagee leads to the same result, but in this manner the inside
of one valve appears as its outside and this creates a false impression; the
correct image can be obtained only by turning the original).
Example 3 (Fig.5): Sketches of Nitzschia sigma valves or another
large sigmoid Nitzschia species are prepared in the same manner as before.
Uhile the mirror image matches in its outline the sketch on side 4,
the conceiled raphes(indicated by the keel puncta) are located on opposite
sides. In order to match their position also, it is necessary to turn the
- mirror image (!) by 1800 about the pervalvar axis; hence,the two halves
are antisymmetrical.
1■1111111•1101MIIIMMIM MOM%
Fig.5: Antisymmetry. Nitzschia sigma, outlines of >valves show mirror-image symmetry, but raphes are on opposite sides; turning a by 180° about its axis results in b as mir- ror image.
Fig.6: Torsion'phenomena. a = Surirella spiralis; b, c = Cerataulus turgidus:
However, in the case of antisymmetry, matching pictures can be ob- p.11
tained also by turning lem one valve (not its mirror image) by 1800 about
its pervalvar axis, since, in this manner, the internal and external views il,
are not switehed a-rou:nd, and there€ore, OLLER's l.nterpretations regar-
ding diagona). synunetr.y ond antisynmet.ry cari be replseed by a simpler epm-
mon formula. Bach pa3-r of frustule halvs,divided by gne seetipn,always
has one axis in common 3ahile the two remaining axes either fnaiçe a parallel f pair or run transversaily to otie another, Thus, the Pervalyar aKis is and El common to halves that are divided by the var plane,^ the transapieal axis to those divi.ded by the apical plsne, ilenee, eases ether than mi.r_ 0 ror-image symmetry may be summarized as foiiows; When deaiing with dia- gonal symmetry, one hali: of the frustule is turned by i80° about one of
the axes that are not eommon to both halves, while, in the ease of 4rit3-
symmetry, one hal-f is turned about the axis eo^unon to both liaives; anti-
symmetry is a eopnlii^a-ion of ^nirrOr=iinage and diagonal syr^Metry,
Examole 4 (Fig.2, p.7); Asymmetry 9pp13-es to all frustules whose
halves have a heteropolar axis in eomnion,
The afore?ner^tioned t^^es represent only the main gFoups, but they
are of guidance also in understanding thep intermediate forms ^akiçh are due
to torsional jnanifestations (Fig.6, p.10). All conditions of sym-
metry relate,of çourse,strictly to one plane only so that a frustule may
simultaneously feature different types of syc^metry (Fig.3, p.8t Eunotia,
mirror-image symmetry in relation to valvar and transapiçal planes, but a-
symmetr-y-in relation to apical plane).
In addition to the valves and the çonnective zone, still other
structural components of the cell wall exist in many Diatomaceae)whiçh
also participate in the enlargement of the frustule in longitudinal direc-
tion. They are inserted between valve and çonaective zone ând are, there-
fore, referred to as inte.rstit3al bauds or "sopulae" (F3g,7, p.12__). Their
Translator's note: In some Fnglish publicat^flAS -also referred. to --..._. .._. - _--- ^---- as l'eonneçting bands. " - 12.
of the valve, but they LI outlines follow of course in most cases the form are not intergrown Tiiith the valve or the zone; instead, the bands are
conneèted to these and other .parts of the frUstule only by folds, forti- o fied ridges, or closely adjacent bladelike edges. The number of bands varies greatly in different species. Some diatoms are consistent, in for-
ming only one connecting band for each half of the frustule, while other n . species feature many such structural parts. Their form is equally vari- able; it is about circular if the bands are extended over the entire ra-
dius of the -frustule while, in other cases, it may consist of several rows p.1
of imbricated scales arranged in pervalvar direction. Circular bands are,
as a rule, open at one end; in the case of several bands, open and closed
ends alternate so as to prevent bursting of the frustule when internal pres-
sure is growing strong. n . Fig.7: Interstitial bands. a = circular (Rhizosolenia); b = scalelike (Rhizosolenia);
. c-k = with septae (c-e Tabel- laria, f-h Tetracyclus, i,k Mastogloia).
IMI.211.7.3.12.17.ii ...Tel
Fig.8: Grammatophora with undulate septae. 0 13.
In numerous diatoms, the ringlike bands extend special partitions
X more or less deeply into the inner cell which run usually parallel with the 0 surface of the valve, or form, in other instances, a narrow band of small compartments usually extending from one end of the frustule to the other,
but sometimes confined to the central part of the valve's margin. These
partitions,originating from the bands, are called "septa" (Fig.7, p.12);
their form varies from straight to undulate (Fig.8, p.12), and they some- 0 times end.in,a hooklike curve; in most cases the septa start only from one (the closed) end of the connecting band, but sometimes they penetrate
the entire frustule and are then more or less perforated to avoid obstructing
the connection between the plasmatic cell contents. They grow before or
even during silicification,starting at the connecting bands, and from the
outside inwards. Whenever parts of the septa meet in the center, more
or less pronounced diaphragms are formed. In certain species the ends of u the valves show similar formations, e.g., at the poles in some species of the genus Stauroneis (Fig. 9). I call these structures "pseudosepta" *
so as to distinguish them from the true septa which are of greater im-
portance in'systematics and are direct extensions of the interstitial bands. k
Fig. 9 p. 13 r, Pseudosepta * at the ends of the valves in Stauroneis. ^'}
Fig. 10: ^., a Meloseir'&`dickiei with inner valves; b craticular plate of Navicula cuspidata.
:1 h ',7t'
Translator's note: Called "diaphragms" in pertinent English publications. The author, throughout his book, writes "Melosira"; -however, this c;enus should be spelled ' e oseira" 14.
Unfavorable environmental conditions, e.g.,-desiccation of the
habitat, leads in some species increasingly fi.o.:,the formation of internal
valves due to incomplete cell division;•-theÿ arè,.therefore, reminiscent
of the resting spores in other species. The best-known example exists in
Aieloseira dickiei (usually inhabiting moist mountain rocks and roofs) in
whicli a varying number of internal valves, stàcked like ice-cream cones, .^ , can, then, be observed (Fig.10a, p.13), while individuals living in water-
rich surroundings do not show any such formation. Of an entirely differ-
ent nature are the peculiar siliceous scaffoldings which grow as an inner
stratum parallel with the valves they are frequently found among forms of
Navicula cuspidata, and known as craticular plates (Fig.10b, p.13). Some
investigators believe that their formation is due also to changes in the J concentration of the surrounding medium. It is possible that they are in- duced by environmental changes, but here, the result differs considerably
0 from the internal valves, and the craticular plates are often enough ob-
served in specimens from areas where environmental changes have not taken
place. However, most striking is,the fact that division of a cell featur-
ing such craticular plates results in a completely new form which is fully
developed and, hence, viable,but entirely.different in the-arrangement.oF
the structural elements from the mother frustule; viewed separately and
without knowledge of the craticular plate phenomenon, the new frustule
could doubtless be mistaken for a separate species. By contrast, the in-
ternal valves are incapable of forming separate viable frustules; instead,
they undergo reduction within the-frustule as their number increases.. Frus-
tules resulting from craticular plates are. - according to my observations -
highly suggestive of mutation, and the biological role of craticular plates 15.
is, in my opinion, hardly comparable to that of the internal valves.
The cell contents consist of plasmatic components which will be
discussed in detail later (p. 34).
Structure of the cell wall
The cell wall of the Diatomaceae consists--in addition to the
siliceous membrane which is probably made up of an opaline silicen com-
pound--also of a pectinous coating. MANGIN assumed that the pectinous
substance were.intimately combined with the silicon compound, and this
despite the fact that he successfully separated it in the form of a pee-
tinous membrane from the silicic acid part: However, LIEBISCH, a former
student of G. KARSTEN, proved about three decades ago that the pectinous
substance forms an independent membrane on the inside of the siliceous
wall to which it is closely fitted. Upon removal of the siliceous stratum
with hydrofluoric acid, its structure is still recognizable on the resi-
dual pectinous membrane and it is, therefore, possible that the latter
projects also into the vacant spaces and pores as far as these are ac-
cessible from the inside. The existence of the pectinous membrane is of
considerable importance to the Diatomaceae, and helps us to understand
many of the otherwise inexplicable, or fallaciously interpreted, phenome-
na such as the extravasation of plasma from thQ mothe.r frustutes during
auxospore development, or the absolute cohesion of individu41 frustule
components despie their noncoalescence and Lhe ofte-u QI.I.HWral.2te inter- ri nal pressure. But it also renders obsolete the theory of tne ulax.ipill and minimum sizes of pores which had been develQped before dlsçovçry of the
pectinous membrane and advocated chiefly by 9tto dLLER.
Upon sufficiently high magnification almost 4“ si1Lc.eou membanes
of the Diatomaceae show some markings and it is questionable w.4.Lber trti 16. ly homogenous membranes really exist. Since the valves are not stained, so that there is no chance that the structural images could be created by the various hues, the markings must be attributed to the alternate suc- cession of dense and less dense, or completely perforated,membrane sec- tions. The denser parts absorb more light than structures of lesser den- sity and they appear, therefore, dark under the microscope when the sur- face is turned toward the observer ("high focus"), whereas less dense structures, having greater translucency, are shining up brightly under high focus. Upon viewing the lower-situated inner surface ("low focus"), the situation is reversed: Denser parts aPpear bright because light is retained, while structures of lesser density appear dark. As a "rule of thumb‘," this optical reaction must be taken into consideration in all structural examinations since it permits - a comprehensive analysis of the microscopic picture. However, it is an important requirement that a sing- ly refracting medium is employed for such examinations (most substances commonly used for mounting meet this requirement; the newer synthetic products are always to be tested beforehand as to their optical proper- ties!),-since birefringent resinous media would of course reverse these effects. Furthermore, to avoid misunderstandings it must be emphasized that, when we speak of "dense" and "less dense" membrane structures, these terms are not to be confused with "thick" or "thinner" since the "thick- ness" of the frustule wall has nothing whatsoever to do with it. Dense areas may sometimes be thinner than adjacent areas of lesser density be- cause they contain cavities. Therefore, the term "dense" implies "mass. density" of which there is less at hollow parts of the wail than where the membrane forms the partitions that divide the cavities. The optical manifestations just described lead us now to the following fundamental - 17.
concept: The structure of diatom membranes is,foremost^a consequence
(or "function") of differentiation of the mass-denGity throughout the
frustule wall.
The denser parts of the wall - at least those of the valves -
seldom develop into areas but are, as a rule, seen as narrow, bandlike
markings forming straight or irregular, very often zigzagging, striae;
frequently, they are very narrow and appear then in the microscopic pic- F-1 ture as "lines". However, regardless of their width, I shall refer to.
them uniformly as "costae." Membrane parts of lesser density show great
variation not only in their form which depends upon the arrangement of
the costae, but also in their finer structure with which the following a in form pages shall deal at leastA of a basic outline. Already for nearly a cen-
tury have scientists labored to analyze their microscopic findings and to
construe from them the true structure of the frustule wall. Most of the
investigations were limited to the fine markings of Diatomaceae which made conducted ideal test objects, but these were usually •, , for the sole purpose of
testing one or the other lense system for its resolving power. Particu-
larly detailed discussions ensued concerning the structure of Pleurosigma
angulatum and many a word was written for or against one or the other con-
cept until Ernst ABBE, the famous mathematician of the Carl-Zeiss-Company*,
finally pointed out that all arguments were fruitless because of the phe- W nomena of diffraction which were not yet analyzable and interfered when-
ever the minuteness of the structure exceeded certain limits. During the
last three decades of the past century it was primarily Otto MÜLLER who, p. 15 n with exact methods (as far as this was possible with a compound microscope),
elucidated the structure of the frustule wall of a number of Diatomaceae,
mostly of the more robust species. Since then, only the author of the
*) Translator's note: In Jena, Germany, at that time. 18.
present publication has offered substantial contributions to this aspect,
which were also based on methodically conducted investigations. With the
construction of the electron microscope this work has entered into a new
phase, and during recent years numerous papers have been published featuring
equally numerous, sometimes more or less good, but often excellent photo-
graphs of Diatomaceae obtained with the ultramicroscope. However, although
with its help further advances have become possible in-the knowledge of
the finer structures of frustule walls, it must be said that the results
obtained with compound microscopes.by those men_who seriously studied the
subject,have, in essence,.â.lmost exclusively'been confirmed. The results
obtained with compound microscopes,as well as the electron-microscopic
photographs,reveal yet another basic fact concerning the construction of
the frustule wall: Every structured siliceous membrane of a diatom con-
sists of a network of siliceous costae forming intricate ramifications of
pores, puncta, and cells. The depth of focus of the ultramicroscope is 0 an undesirable feature in this kind of work since it makes it impossible to analyze thicker objects (which the siliceous membranes represent) on nt the basis of a series of horizontal sections which alone could give us an idea of their physical aspects. Furthermore, even the electron micro-
^ scope does not eliminate diffraction so that, with certain structures, w we have to expect interference patterns. Hence, photographic illustra-
T. tions present not only all aspects of the frustule wall.from the inner
to the outer stratum, but possible interference patterns may also enter
the same field and will,of course,show up in such photographs also when
viewed stereoscopically. Whether they will then be distinguishable from
true structures cannot, offhand, be taken for granted in all cases, and many a 0 19. picture of membrane structures obtained in this manner may hardly corre- spond to reality. Many microscopists will also have occasion tà. study electron-microscopic photographs, and I have > therefore,deemed it neces- sary to point to such possible errors.
Since the ultramicroscope has furnished proof that the structural elements -- as far as they lent themselves to examination -- which appear under the compound microscope as "puncta" or "areoles" are closed at least on one side by pellicles, the question arises whether true perfora- tion really does exist in the valves of Diatomaceae. The answer has to be confirmative, because true perforations are: 1. The raphe (to be dealt with in detail in the next chapter, p.25), 2. the "mucousnor "gelatinous pores", 3. the "interstitial mesh" seen in some of the Centricae, 4. the
"isolated dots" in the central area of many species among the Pennatae.
Fi.11: Gelatin pores. a = Stephanopyxis with hollow processes*; b,c = Eunotia, gelatin pores in the coleoderm; d = Synedra, porus near end of valve*; e = Tabellaria, porus near center of valve*.
*) Translator's notes: a = processes described as "crown of spines" serving concatenation, in Synopsis of North American Diatomaceae; d,e, "terminal" and "median pores", respecti\re- ly.
Gelatinous or mucous pores are found mainly in colony-forming species where they provide the material for the connecting substance, but they may occur also in other forms in which concatenation or sessile existence 20.
are unknown. Very extreme structures of such nature can be observed in
some marine genera, e.g., Stephanopyxis (Fig.11a, p.19), where they form
longer or shorter,extrafrustular, hollow processes which probably secrete
the agglutinant wich holds the processes of adjacent frustules together and, n. thus, conects them to chains. However, in most cases, the gelatinous po- res are minute,cone-shaped, pierced, projections into the inside of the
frustule, and have a fixed position in individual species. In the Centri- E . cae they are usually located close to the valvar margin but often also at about the center of the valve; in the Pennatae they are nearly always
I D seen close to the poles, either on one or On both ends. Very seldom are ge- latinous pores observed in the center of the valves in the Pennatae, un-
less the so-called "isolated dots" of many species (to be discussed below)
should also be considered as àelatinous pores Easily spotted are the gelat-
inous pores in the larger species of the genus Synedra which, as a rule,
feature one porus in the valve close to one pole (Fig.11d, p.19). Less
easily recognizable is the porus in the Eunotia species because, here, it
is usùally embedded in the plication of the valvar pole, and hence, it
becomes visible only under low focus (Fig.11 b, c, p.19).
17.3WP2ert›-: Fia 12.• "Interstitial mesh" in Coscinodiscus perforatus elrlf.ee'\ 6 ÎM n. 1,r • • k,r1•,'"% . e,•I'hi,•!.:P
•■••■•••••■• The "interstitial mesh" consists of minute "dots", which are more or
less numerous in some Centricae with areolate valves; they can definitely N not be considered as areolation products, that is,- as "remnants" missed by *) Translator's note: Called "cells" in pertinent Engl. publications. R 21. the areolation process, since they are constant in some species, and absent El in others with similar areolation. They are always situated singularly be- 0 fore the shorter radial rows of areoles, and are conspicious not just by their minuteness but also by their enhanced brightness, that is, by greater D translucency which is greatly indicative of membrane perforation. The pur- pose of the "interstitial mesh" is not known, but here too, we may be dea-
ling with gelatinous or mucous pores (Fig.12, p.20).
The term "isolated dots" has been applied,so far^in earlier descrip-
0 tions to structural elements in the central vicinity of the valves of navi- .
cular diatoms. These are sometimes situated close to the central nodule,
in other instances they may appear in front of the central structural columns 0 and give the impression of constituting scattered parts of the normal struc- ture. They are observed mainly in the genera Navicula, Cymbe.lla, Gomphonema,
0 and Gomphocymbella; their position and usually also their number are con- 0 stant in most species, only a few forms show slight fluctuations in their number. As far as I could examine these structures - which is the case in
{! almost all species in which they occur -- they were identifiable as orifices
of canaliculi. Their true nature is best visible if their course through
0 the valve has a slightly sloping angle since they are then seen in full LI length and the differentiation betwèen outer and inner orificès becomes quite apparent (Fig.25b, p.37). However, in many cases, the canaliculi
run vertically through the frustule wall and are then not always easily
recognized as such, particularly when their position is just in front of
other striate markings (Fig.13, p.22). However, here again, true canaliculi
always give their presence away by their greater translucency, that is, by
p.17 enhanced brightness; when in doubt, a greater number of individuals of 0 the same species will have to be compared to establish whether the case in question represents a constant feature or merely an incidental struc- 0 0 22.
tural anomaly. In some spéci;es,- the dériâliciili âré extremely delicate
and the position of the ori^fi:c-es 6t flïé déritrâl rifldtrle can often be
established only with the-he-1-g of liiglï-lÿ r-efrâctivie- mounting medià, so
that they were discovered ônl-X quite r'-"6d6ntlÿ in a numbér of-'species.
Since they are, as mentioned- a-bôve; i dôristânt feât-ure of the relevant
species, they constitute a 156sW di-stiftgüi-shing mark in the identification
of species. Their purpose âlsci réinérns dbscuré; but most probably we
are dealing here again with g-6l,dtinôüs ôr ffihéôus pores; however, the
question as to the time of th-ëïr âctivitÿ = whether during concatenation
or auxospore formation - fèmdins ünânswéréd: Vèrÿ conspicuous in this
respect is the position of t-lïé CânâlïÉÜli in sôüië species. While, as a
rule, both orifices lie at t13(f i-rI§idé ô€ the valvé; the inner orifice (e.g., 0 in Navicula lagerheimii) MAY fd-téin tltis-pôsi€iôn iahile the outer orifice is situated at the margin ôf tlïé valve Aéfé It lads over to thezone. filaments 0 This species forms du'rfng its végé€â€ivé existence and this fact may have something to do with thè pôsiEiôn ô€ €Iié cânalicular orifices. I 111sé1atéd dots" ÿmbella x b = G6mphonema c = KaYicula
a F.ig.14: Longitudinal sections through cells of Triceratium; à= cells open on inside and closed on outside, b = reversed. ^ ) q A= outside ^.( J= inside j K= cells
The actual structure of the frustule wall consists of the network
of--costae; the enclosed spaces cân be described as "cells" although, in many 23.
instances, they merely form slight indentations. In the literature they
are usually described as punctae, areoles, or dots, depending upon their
size and form. According to the electron-microscopic findings it is highly
unlikely that cells exist which are open on either side, toward the inside
of the wall as well as toward the outside; all alveolar cells will be
covered at least on one side by a membrane which has, however, a certain
porosity. The other side may be completely open, or may,as a consequence
of T-shaped thickening and broadening of the costae (Fig.14, p.22), show
correspondingly narrowed openings; furthermore, since the costae differ
in thickness, particularly the larger cells may be divided into smaller
ones, so that KOLBE prefers to distinguish four types of areolar cells:
1. Undivided open cells, 2. divided open cells, 3. undivided, partially
open cells, 4. divided, partially open cells (instead of "divided" and
"undivided" distinguishes KOLBE between cells of the 1st and 2nd order),
The position of the porous membrane and the open or partially open cell
partitions varies; in many species the cells are open toward the outside,
in others -- probably in most -- the openings are at the inside. Size,
form and distribution of these cells depend upon the course taken by the
costae; a few examples shall be discussed in greater detail:
a) One system of costae only, running in transapical direction; genus Pinnularia (Fig.16, p.26). The costae extend from the zone to the median line of the valve which runs in apical direction, and protrude more or less deeply in pervalvar direction inside the frustule so that groove-
like cells are formed whose outer cover has been established, electron- microscopically, as a porous pellicle (open cells of the fst order). In many species of this genus, the inner endings of the costae are broadened in T-shaped fashion so that the cells have only a fissurai opening toward p. 18 24.
the inside (partially open cells of the lst order); in valve view, the
openings appear as a more or less wide band,crossing the costae. Some spe-,,-.:
cies of other genera (Caloneis, Diploneis) feature not just one but several
openings to the inside.
b) Valves with two crosswise arranged systems of costae (Figs. 9,
p.13, and 13, p.22). Apparently, this is common to most Diatomaceae; it
results in the formation of "puncta" which usually show, upon sufficient shape. magnification, a polygonal to circular^ As far as is known, these puncta
also represent porous membranes. We are dealing here with the outer walls
of more or less deep cells on the inside of the valves which are again ei-
ther completely open or show only a narrow opening toward the inside (Di-
ploneis).
Fig.15: Pleurosigma with three crosswise arranged systems of costae.
c) Valves with three crosswise arranged systems, structural type
according to Pleurosigma (Fig.15). The minute cells have a polygonal (hexa-
0 gonal) shape and are closed on one side by a porous membrane, but it is
not yet decided whether on the inside or the outside. According to electron-
microscopic photographs, the opposite side has,allegedly,. fissuriform ope-
nings in apical direction; however, definite proof has not yet been ob-
tained as.to whether we are dealing here with completely open cells or if
this impression is due merely to diffraction images.
d) Twin-rows of areoles between the costae. In addition to the r
25. jD strong costae there are formations of finer striae So that the interstices
are dissolved into more or less delicate areoles-. They may occur in valves
having a single (transapical or radial) system as well as in those having
multiple systems of costae, and result in open or partially open cells of
the 2nd order. Diploneis diplosticta (GRUN.) might be considered as one
of the best examples. The cells formed by two primary, strong systems of
costae are divided by delicate secondary striae into smaller areolar cells
which are in.contact with the contents of the frustule by way of common
D. - circular openings on the inside of the valve (partially open cells of the
2nd order).
e) Areolate structures of the Centricae (Fig.12, p.20). As a rule, E there exist three systems of costae, one running radially, the other two taking a tangential to spiraling course so that polygonal areoles are for-
med which correspond to the outer and inner walls of polyhedral cells. A
porous membrane is formed either by the inner or the outer wall (either
case is possible!) while the opposite wall usually has a central circular
opening, in other words, it is partially open. Hence, radial rows of cells
are, strictly speaking, just "Pinnularia cells" subdivided by transversal
partitions into smaller cells; this division is manifest already in many
Pennatae without being indicative of any phylogenetic relationship.
Despite the considerable variability in the structure of Diatoma-
ceae valves, the structures can,most likely,in all cases be compared with
the types discussed; however, this requires an intelligent analysis of the
microscopic picture, based strictly on facts. [1 Raphe and motility The raphe, featured by only one group of Diatomaceae, is in its. ri original form a cleftlike division of the valve and must be considered 111 26.
strictly as an organ of locomotion. That it indeed serves exclusively
this purpose and has no part in metabolic functions is evidenced by the 0 reduction phenomena observed in those cases in which motion is abandoned in favor of sessile existence or concatenation. For example, in those
Cocconeis species that rest on a substrate, only the adherent valve pos-
sesses a raphe, while the unattached valve has lost its raphe. Similarly,
0 Navicula species changing to concatenation or sessile existence are known 0 to start losing their raphe completely or partially. The raphe remnants, frequently seen in unattached Cocconeis valves as well as in the Navicula 0 species mentioned,are proof that we are dealing here with true reductions. A shift of the raphe from the valve to the zone or the valvar margin (e.g.,
0 Eunotia) is due to similar causes.
0 Fig.16: Raphe of Pinnularia; a = valve view, b, d = ends of valve, c= center of valve, e = central nodule (slightly schematized). R raphe, Z = central nodule, Ek = terminal nodule, Ar = exterior channel of raphe, Jr = inner channel of raphe, P = terminal fissures, T = infundibulum, A z-- éxterior.median pores, Jzp = interior median pores, 0 Zr = open groove at central nodule, Zk.= channels at central nodule. 0
Fig.17: Frustulia Raphe with lateral project-L•ons at median pored and before terminal fissures. 0 27.
The progressive changes in structure and position of the raphe which evolved in the course of development have become of vital impor- tance in systematics. The two main types, the "Pinnularia raphe" and the
II concealed raphe," . have been described in detail mainly by 0. MULLER and
R. LAUTERBORN; additional investigations, particularly those concerned with the phylogenetic development, were in essence initiated by the author of the present publication. Apart from keeled and alate raphes is the Pinnularia raphe (Fig.16, p.26) the most progressive stage of develop- ment of this organ so that it seems appropriate to base our discussion on this form. Large individuals of PinnulAria viridis (NITZSCH) EHRENB. occurring nearly everywhere or any other large species of this genus may serve as illustrative object. Along the median line of the valve we see a more or less composite and twisted, centrally interrupted, system of lines. It is surrounded by a blank longitudinal field called the "axial area" which widens in the middle to form the central area. The lines define the cleft which divides the valve and is known as raphe. How- ever, the plane of cleavage shows interruptions and windings, the edges of the two valvar halves are interlocked by folds so that the single cleft is divided into the so-called exterior channel and the inner channel which open to the outside and inside respectively. Examination of the frustule in zone view shows that the aforementioned central interruption consists of a thickening of the mèmbrane extending as a cone inward, and designa-
ted as "central nodule." Both branches of the raphe terminate in the cen-
tral nodule with a tubular widening, the "central-nodular channels," the orifices of which are distinguishable, in valve view, as 'exterior and
interior median pores. An open groove, embracing the central nodule in a
semicircle, the "central-nodular groove", connects both branches of the 0 0 28.
raphe. Nodular structures are visible also on either end of the valve,
especially in zone view; these are the terminal nodules which,.in are contrast to the central nodule „ hollow. The exterior channel of the il raphe runs through the outer wall of the terminal nodule whereby the
plane of cleavage, the "terminal fissure," describes more or less spi-
raling windings, usually bending in a wide curve; the inner channel of
the raphe enters the terminal nodule from the inside, ending abruptly in
a spoutlike infundibulum.
Similarly complicated raphe structures can be found in several
other biraphe-bearing diatoms, especially also of the genus IMastogloia.
However, even within this group, we find conditions often much more simp-
lified whereby individual parts are distinguishable only with great diffi-
culty. The plane of cleavage is seldom interrup'ted,_the exterior and
inner channels of the raphe are superimposed .(threadlike raphe), or the
raphe enters the valve in an oblique angle and appears,therefore, in valve as view more or less A broad area, the terminal fissures are often very minute
or are replaced by a simple porus, and.sometimes, slitlike.lateral pro-
jections are seen at the median pores (very seldom also before the terminal
fissures). All these factors play an important part in systematics and
deserve, therefore, special attention in all examinations (Fig.17, p.26).
It is equally important to consider the position of the median pores as
well as that of the terminal fissures which are located either in continued 0 direction of the channel of the raphe, or may take a turn in either the same or in opposite directions.
Since, in addition to the Diatomaceae possessing a raphe, many
species exist without this organ, we are faced with the question where to K look for the initial stage of this structure and in what form. This prob- 29.
lem presents itself particularly in the Rhaphidioidineae group which in-
cludes the genera Peronia, Amphicampa, Pseudohimantidium, Eunotia and
Actinella. All species belonging here are characterized by a very short
partial raphe at the ends of the valves in which nodule formation is sel-
dom observed or only poorly developed (Fig.18) so that it must be assumed
that the first raphe clefts developed from a porus which expanded towards
the center of the valve. A certain difficulty arose from the position
of the raphe, since, in the genera Eunotia and Actinella, the greater
part of the cleft is located in the zone, and, in most species, little of
it projects into the surface of the valve,.namely only at the terminal no-
dule; however, in some species, a prolongation of the external channel
beyond the nodule . may be observed either toward the dorsal margin of the valve or, retrogressively, parallel with the ventral margin of the valve.