IAWA Bulletin n.s., Vol. 3 (1),1982 3

ANTONI VAN LEEUWENHOEK AND HIS OBSERVATION ON THE STRUCTURE OF THE WOODY CELL WALL

by

Pieter Baas Rijksherbarium, Leiden, The Netherlands

Summary Following general remarks on the life of Van be traced back to negative but ill-informed Leeuwenhoek and his role in wood anatomy, judgements in some authoritative 19th and his account of the structure of a torn vessel 20th century publications (Baas, 1982a, b). wall of nutmeg rootwood is discussed in detail. Van Leeuwenhoek should be credited with The cross-wise orientation of minute 'vessels or many detailed and original wood and bark ana­ fibres' as observed and interpreted by Van tomical observations, but his work is not easily Leeuwenhoek can be considered to be the first accessible, being scattered in numerous letters, (unintentional) correct record of the fibrillar most of them also dealing with other microsco­ nature of the woody cell wall. pic subjects. Although most of these letters were published in various instalments and sev­ Introduction eral languages during Van Leeuwenhoek's life­ Antoni van Leeuwenhoek was born in 1632, time, this presentation cannot compete with 350 years ago, in Delft (the Netherlands) as the the balanced treatises by Grew and Malpighi, son of a basket maker. Apprenticed to a cloth who each published books solely dealing with merchant, Van Leeuwenhoek's career started as plant structure and function. a shopkeeper. Later he would serve as usher to Interest in Van Leeuwenhoek's plant anato­ the aldermen, chief warden and wine-gauger of mical work has recently also been revived by the City of Delft, and surveyor to the Court of the rediscovery of some of his sections among Holland. Van Leeuwenhoek's scientific life his correspondence to the Royal Society (Ford, started late, at the age of 39 when he developed 1981a, b, c, and this issue). Van Leeuwenhoek's his first, simple microscopes. His microscopic free hand sections of cork and elder pith ap­ observations are recorded in an extensive corre­ peared to be of such excellent quality, that spondence with the Royal Society of London they still allow critical observation with the and with individual scientists, which Van Leeu­ modern scanning electron microscope, without wenhoek continued until his death at the age showing sectioning defects. of 90. His observations and interpretations This note only highlights one aspect of Van would rightfully earn him contemporary and Leeuwenhoek's immense work on the structure lasting fame as a pioneer in several biological and function of wood, viz., his admirable ob­ disciplines. Especially his discovery of micro­ servations on the structure of the woody cell organisms, his microscopic observations on wall. For further information the reader is re­ blood circulation, and of spermatozoa through­ ferred to the annotated edition (in English and out the animal kingdom stand out as land marks Dutch) of Van Leeuwenhoek's letters (1939- in the history of biology. Throughout his active present; still in progress) and Baas (198Ia). In­ scientific life, Van Leeuwenhoek also concern­ teresting data on Van Leeuwenhoek's micro­ ed himself with the anatomy and physiology of scopes can be found in Van Zuylen (1980). plants, but in these fields his achievements are General data on Van Leeuwenhoek and his usually considered to be far less important than, work are amply provided by Dobell (1932), and in fact inferior to those by Marcello Malpi­ Schierbeek (1950, 1951, 1959), and Heniger ghi and Nehemiah Grew, the Italian and En­ (1968). A portrait of Van Leeuwenhoek adorns glish 'joint fathers' of plant anatomy. the cover of this year's IAWA Bulletin volume. A comprehensive study of the scattered communications on wood structure and func­ Van Leeuwenhoek's observations on nutmeg tion by Van Leeuwenhoek, and a comparison rootwood with the major publications by Grew (1682) In his letter of I May 1695 (Vol. X of the and Malpighi (1686) has shown that this under­ Collected Letters edition) to the Royal Society, estimation of Van Leeuwenhoek's significance Van Leeuwenhoek writes at length on the nut­ for wood anatomy is fully unjustified, and can meg seed, embryo and rootwood. At this time

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that the transparent membrane which consti­ tuted the Wood tubule also seemed to be com­ posed of vessels, which also lay in the circum­ K. ference of the Wood tubules. In order to test this, I tore the said large Wood tubes in pieces lengthwise. And then perceived that they were M unusually crenate when torn, from which I firmly concluded that, however transparent those Wood tubules might appear to me, they were surely composed of a large number of ves­ sels running in circles. Fig. 12. IK. (reproduced here) denotes a very minute part of a torn-up and crenate large Wood tube, which Wood tube is very firmly joined to the adjacent small ves­ sel indicated by LM., from which I imagine the large Wood tube has derived its growth, the more so because one sees that, however trans­ parent the membrane of such a large Wood tube appears to be in many places, the large Wood tube is composed of vessels which seem to have their origin in the small vessel. Further I studied several of the aforesaid large Wood tubules as accurately as possible, and then I imagined I saw that the membrane of which the large Wood tube consisted was formed by small vessels or fibres extending crosswise through each other; and this part or membrane is denoted here by LNOI., the vessels or fibres extending therein through each other from I. to N. and from L. to 0., in order to impart some strength and rigidity to such a thin body through this structure; and who knows what different parts more such a Wood tube may contain.'

Discussion Van Leeuwenhoek's figure 12 of his letter of In order to appreciate Van Leeuwenhoek's I May 1695 to the Royal Society of London text it must be realised that he made use of a (reproduced from Vol. X of 'The Collected terminology, based on the belief that virtually Letters'). all elongate microscopic structures observed in the plant body were vessels serving for the transport of (sometimes specific) saps. Thus in Van Leeuwenhoek was already an experienced the illustration reproduced here Van Leeuwen­ wood anatomist: in previous years he had de­ hoek interpreted the optical section of the lon­ scribed fairly accurately the stem anatomy of gitudinal wall LM as a vessel which supplied the some softwoods and several temperate and true vessel with substances necessary for its ini­ tropical hardwoods. One of his first remarks tial growth, and the fibrillar wall fragments is that it appears that the 'trunk of a Tree does seen in (oblique) surface view as minute vessels not have a different structure from the Root.' derived from LM. Here Van Leeuwenhoek's in­ Subsequently he gives a very detailed, well il­ terpretation (admittedly speculative as indica­ lustrated description of the anatomy of Myri­ ted by the words 'I imagined') becomes dualis­ stica rootwood based on transverse, tangential tic: the larger wall fragments between I and K and radial sections, which he concludes with are termed small vessels, but the criss-cross his almost 'ultrastructural' account of the ves­ structure in LNOI vessels or fibres, and for sel wall. The following citation is from the En­ these also a mechanical function is invoked. glish translation (p. 221 and 223) in the Col­ What did Van Leeuwenhoek really see? In the lected Letters: 'I also tried, if possible, to dis­ annotations of the Collected Letters, W. K. H. cover the structure of the large Wood tubes .. ,. Karstens stated that 'It is almost certain that L. during which examination it appeared to me here saw a system of cracks caused by shrink-

Downloaded from Brill.com10/01/2021 02:43:55PM via free access IAWA Bulletin n.s., Vol. 3 (I), 1982 5 ing (Fig. 12. LNOL). The cell wall, in particular solved at the light microscopic level. However, the secondary wall, is composed of thin con­ due to the fibrillar nature of the cell wall layers, centric layers and is well developed in cells splitting or tearing of woody cell walls follows with more or less thick walls, such as they also the direction of the fibrils of the individual occur in the wood. Each layer is composed of wall layers and produces a (macro)fibrillar pat­ cellulose fibrils arranged parallel to each other tern which can be seen at fairly low magnifica­ and extending at an oblique angle to the longi­ tions, both in the light microscope and in the tudinal axis of the element in question. In suc­ scanning electron microscope. Van Leeuwen­ cessive layers of the cell wall such highly hy­ hoek or his draughtsman must have idealised drated fibrils show differences in orientations. this observation considerably in the figure re­ Through desiccation the fibrils shrink so that produced here. Yet his drawing gives a model they grow thinner, and diverge from each other; for the woody cell wall (or cell wall pair) which thus, differences in their orientation become is fairly close to the truth, and can be consider­ visible in a system of cross-wise extending ed a forerunner of modern views on cell wall cracks.' . ultrastructure. Karstens put forward this interpretation be­ Van Leeuwenhoek's contemporary Nehemiah fore the days of extensive scanning electron mi­ Grew also indulged in speculations on cell wall croscopic research of the woody cell wall. To ultrastructure, but both his warp-and-woof my knowledge such research has never led to model for fibres intertwining between individ­ the observation of microscopic cracks due to ual cells and his drawing of the structure of a shrinkage in sound wood, however strongly the conifer tracheid do not bear any relationship specimens were dehydrated in the vacuum with reality (cf. Baas, 1982a). chamber of the scanning electron microscope. It may thus be befitting of the 350th anni­ Therefore Karstens' explanation must be versary of Van Leeuwenhoek's birth to pro­ doubted, unless Van Leeuwenhoek studied claim him not only a co-founder of plant anat­ badly deteriorated wood. Biodeterioration omy, but also a Grandfather of wood ultra­ leads to removal of part of the cell wall matrix structure. substances, and the fibrillar make-up of the cell wall may thus become more easily visible in the References light microscope, especially after dehydration. Baas, P. 1982a. Leeuwenhoek's contributions The possibility of some form of degradation is to wood anatomy and his ideas on sap of course not unlikely if Van Leeuwenhoek's transport in plants. In: Antoni van Leeu­ rootwood specimen remained unpreserved for wenhoek 1632-1982. Studies commemo­ some time in the hot humidity of the tropics. rating the 350th anniversary of his birth There may, however, be a more simple ex­ (eds. L.C. Palm & H.A.M. Snelders). Ro­ planation. Most probably Van Leeuwenhoek dopi, Amsterdam (in press). did all his wood anatomical observations on - 1982b. Systematic, phylogenetic, and eco­ dry sections. Any anatomist who has ever look­ logical wood anatomy. History and per­ ed at unmounted, dry sections will know that spectives. In: New perspectives in wood in this way minor sectioning artefacts such as anatomy (ed. P. Baas). Martinus Nijhoff/ shredded cell walls, but also the fibrillar nature Junk, The Hague (in press). of torn cell wall fragments (mostly split at Dobell, C. 1932. Antony van Leeuwenhoek boundaries between successive cell wall layers) and his 'little animals'. Bale & Danielson, can be observed even at fairly low magnifica­ London. tions (c. 200-300 x, i.e., within the reach of Ford, B.J. 1981a. Found - Van Leeuwenhoek's Van Leeuwenhoek's microscopes, cf. Van Zuy­ original specimens. New Scientist 30 July len, 1980). In liquid or balsam mounted sec­ 1981: 301. tions such details become virtually invisible. In -- 1981 b. The van Leeuwenhoek specimens. dry sections of nutmeg stemwood vessels I have Notes Rec. Roy. Soc. London 36: 37-59. observed patterns similar to, but less distinct -- 1981 c. Leeuwenhoek specimens. Speci­ than the cross-wise structure of Van Leeuwen­ mens from the dawn of microscopy. The hoek's figure between LNOI, but doubtlessly Biologist 28: 180-182. due to the microfibrillar make-up of superim­ Grew, N. 1682. The anatomy of plants with an posed wall layers (or of. wall pairs of adjoining idea of a philosophical history of plants. elements). Shredded wall fragments as pictured Rawlins, London. between K and I can also be observed at fairly Heniger, J. 1973. Antoni van Leeuwenhoek. In: low magnification. Dictionary of scientific biography (ed. C. Of course Van Leeuwenhoek did not observe C. Gillispie) 8: 126-130. Scribner's, New individual microfibrils - these cannot be re- York.

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Leeuwenhoek, A. van. 1673-1696 (1939-con­ 1959. Measuring the invisible world. The tinued). The collected letters I-XI. Swets life and works of Antoni van Leeuwen­ & Zeitlinger, Amsterdam. hoek FRS. Abelard-Schuman, London, Malpighi, M. 1686. Opera Omnia. London. (Re­ New York. printed 1687, Leiden.) Zuylen, J. van. 1980. The microscopes of An­ Schierbeek, A. 1950 & 1951. Antoni van Leeu­ toni van Leeuwenhoek. J. Microscopy 121 : wenhoek - zijn leven en werken. I & II. 309-328. De Tijdstroom, Lochem, the Netherlands.

REVIEW

The study of plant structure: principles and guidelines for sectioning wood. Their observa­ selected methods. T.P.O'Brien and M.F.McCul­ tion that some of the world's greatest practi­ Iy, c. 340 pp. (A4), iIIus., 1981. Termarcarphi tioners of these skills are now dead or retired, Pty Ltd., 10 Arbroath Road, Wantirna, Victo­ and that many of them failed to set down in ria 3152, Australia. Price: Aust.$ 35.00 (hard any detail instructions suitable for a novice, is cover) or Aust.$ 20.00 (paperback); postage perhaps overpessimistic. Excellent wood sec­ and handling: $ 3.00 within Australia, $ 4.90 tions are still being produced in many wood overseas. research laboratories all over the world. One This privately published book offers a wealth useful reference has been overlooked, i.e., B.F. of information on methods available for the Kukachka's 'Sectioning refractory woods for study of plant structure. It is well written and anatomical studies' (USDA For. Servo Res. Note pervaded throughout with a profound under­ FPL-0236, Madison, Wisconsin, 1977, and standing of plant structure and a love for the Micrographia 80: 301-307, 1978). In looking crafts developed over the centuries to unravel for other minor imperfections one might chal­ its secrets. lenge the authors' diagnoses and remedies for Following an introductory chapter on the excessive curling of sections: some woods will study of structure in general, there are chapters always produce curling sections whatever the on microscopic, morphological and anatomical pretreatment, and the only remedy I know of, methods, and on photographic procedures. An is to prevent them in time from doing so with a extensive formulary (103 pp.), several appendi­ brush, and to keep them between filter paper ces, and a long bibliography conclude the book. during staining and dehydration procedures (I The authors do not claim completeness, but owe this trick to Mr. BJ .H. ter Welle). In view have certainly succeeded in producing a useful of the multitude of techniques and tissues dealt source of methods and approaches. Simple with, a general index is seriously missed. methods are favoured, and several methods de­ The book is well illustrated and includes scribed in the older German literature are re­ some beautiful colour plates. One wonders why vived. This is to be welcomed, in view of the it was printed on A4 size with a direct repro­ general neglect of German (and French) litera­ duction of the typed manuscript. Considering ture in English speaking countries. this, the book is still fairly expensive. It cer­ The account of microtechnical methods to tainly deserves a wide enough circulation to be used in wood anatomy is of interest, since justify more sophisticated type-setting and the authors confess that they had no direct ex­ publication at a modest price by an interna­ perience in the field and found considerable tional firm. Meanwhile praise is due for this first difficulty in finding information in the litera­ edition which will be invaluable for beginning ture. Considering this drawback, they have done and experienced students of plant structure. very well in unearthing the most important Pieter Baas

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