History of botany (1530–1860)/Book 2/Chapter 1

by Julius von Sachs

CHAPTER I.

Phytotomy Founded by Malpighi and Grew.

1671–1682

The foundation of vegetable anatomy, indeed of all insight into the structure of the substance of plants, is the knowledge of their cellular structure. We find the first perception of this truth in a comprehensive work of Robert Hooke^[1], which appeared in London in 1667 under the title of 'Micrographia or some physiological descriptions of minute bodies made by magnifying glasses.' The author of this remarkable book was not a botanist, but an investigator of nature of the kind more especially to be found in the seventeenth century; he was mathematician, chemist, physicist, a great mechanician, and later an architect, and moreover a philosopher of the new school then rising. Beside many discoveries in various subjects he succeeded in 1660 in so far improving the compound microscope, that with considerable increase in magnifying power it had tolerably clear definition. With this instrument Henshaw in 1661 is stated to have discovered the vessels in walnut-wood, a fact not of importance for our history. Hooke himself was anxious to show the world how much could be seen with his improved instrument; as an adherent of the inductive method he desired to aid in perfecting the perceptions of sense which are the foundation of all human knowledge; with this feeling he submitted all sorts of objects to his glass, that it might be known how much the unassisted eye fails to perceive. He made what he saw texts for discussions on a multiplicity of questions of the day. The book therefore was not devoted to phytotomy; the structure of the substance of plants is noticed in the same incidental manner, as the discovery of parasitic fungi on leaves, or other similar matters. And what Hooke saw of the structure of plants was not much, but it was new, and on the whole fairly judged. It appears that he discovered the cellular structure in plants by examining charcoal with his glass, and that he then tried cork and other tissues. He says that a thin section of cork on a black ground (by direct light therefore) looks like honey-comb; he distinguishes between the hollow spaces (pores) and the dividing walls, and to the former he gives the name which they yet bear; he calls them cells. The arrangement of the cork-cells in rows misleads him into taking them for divisions of elongated hollow spaces, separated by diaphragms. These, he says, are the first microscopic pores, which he or any one else had ever seen, and he regards the cell-spaces of plants as examples of the porousness of matter, as do the text books of physics up to modern times. Hooke employed his discovery especially to explain the physical qualities of cork; he estimates the number of pores in a cubic inch at about twelve hundred millions. He draws another botanical conclusion; he gathers from the structure of the cork that it must be an outgrowth from the bark of a tree, and appeals to the statements of one Johnston in proof of this hypothesis. The fact, that cork is the bark of a tree, was therefore not yet known to all educated people in England. Hooke afterwards says that this kind of texture is not confined to cork; for as he examined the pith of elder and other trees with his microscope and the pulp of hollow stems, such as those of fennel, teasel and reed, he found a similar kind of structure with the difference only, that in the latter the pores (cells) are arranged lengthwise, in cork in transverse rows. He says that he has never seen any passages for communication between the cells, but that they must exist, because the nourishing juice passes from one to another; for he has seen how in fresh plants the cells are filled with sap, as are the long pores in the wood; but these he found empty of sap in the carbonised wood, and filled with air.

It is plain that it was not much that Hooke saw with his improved microscope; thin cross-sections of the stem of balsam or gourd, two plants that grew at that time in every garden, would have shown the naked eye as much or even more of vegetable structure. At the same time there is proof here of what was said above on the influence of the microscope on the use of the eye; the pleasure in the performance of the new instrument must first direct attention to things which can be seen without it, but were never seen.

About the time of the appearance of Hooke's 'Micrographia' Malpighi and Grew had already made the structure of the plant the subject of detailed and systematic investigations, the results of which they laid before the Royal Society in London almost at the same time in 1671. The question to which of the two the priority belongs has been repeatedly discussed, though the facts to be considered are undoubted. The first part of Malpighi's large work, the 'Anatomes plantarum idea,' which appeared at a later time, is dated Bologna, November 1, 1671; and Grew, who from 1677 was Secretary to the Royal Society, informs us in the preface to his anatomical work of 1682, that Malpighi laid his work before the Society on December 7, 1671, the same day on which Grew presented his treatise, 'The Anatomy of plantes begun,' in print, having already tendered it in manuscript on the eleventh of May in the same year. But it must be observed that these are not the dates of the larger works of the two men, but only of the preliminary communications, in which they gave a brief summary of the researches they had then made; the fuller and more complete treatises appeared afterwards; the preliminary communications formed the first part of the later works and to some extent the introduction to them. Malpighi's longer account was laid before the Society in 1674, while Grew produced a series of essays on different parts of vegetable anatomy between 1672 and 1682; and these appeared together with his first communication in a large folio volume under the title, 'The anatomie of plantes,' in 1682. Thus Grew had opportunity to use Malpighi's ideas in his later compositions; he actually did so, and the important point as regards the question of priority is, that where he makes use of Malpighi he distinctly quotes from him. No more is necessary to remove the serious imputation which Schleiden has made against Grew in the 'Grundzüge' (1845), i. p. 207.

Whoever has not himself read the elaborate works of Malpighi and Grew, but knows them only from the quotations in later phytotomists, may easily imagine that these fathers of phytotomy had found their way to a theory of the cell, such as we now possess. But it is not so; their works have very little resemblance to modern descriptions of vegetable anatomy; the difference lies chiefly in this, that modern writers in their accounts of the structure of plants start with the idea of the cell, and afterwards treat of the connection of cells into masses of tissue. The founders of phytotomy on the contrary, as might naturally be expected, consider first and foremost the coarser anatomical circumstances; they describe the rind, bast, wood, and pith chiefly of woody dicotyledons, and the histological distinctions between root, stem, leaf, and fruit in their broader relations, and examine the detail of the structure of buds, flowers, fruits, and seeds for the most part only so far as it can be seen with the naked eye. The more delicate structural conditions are afterwards discussed as a supplement to this less minute anatomy and always in close connection with it. The chief emphasis is laid on the consideration of the way in which the fibrous tissue connects with the succulent parenchyma, while such questions as the nature of the cell, the fibre, and the vessel are only incidentally touched upon or discussed at greater length in the course of the exposition. The mode of investigation and exposition is therefore chiefly analytic, while in modern compendiums of phytotomy it is essentially synthetic. It need scarcely be said that with this mode of treatment the questions which are now regarded as fundamentally important are either treated as of secondary moment, or are disregarded; we must not therefore, in judging of the merit of these men, approach their works with the demands upon them which our more advanced science would lead us to make. It would be quite wrong even to think of measuring the value of their books by the extent to which their contents agree with the modern cell-theory. Both of them had enough to do to find their way at all in the new world which the microscope had revealed; many questions which have become trivial for us had then to be solved for the first time, and the chief merit of both lies in this very effort to understand first of all the coarser relations of the anatomical structure of plants; in this respect the study of their works may yet be recommended to beginners, because modern phytotomical books are generally very imperfect on these points. And yet we must not undervalue what Malpighi and Grew had to say on the more delicate anatomy, and especially on the nature of the solid framework of cell-membrane in the plant; imperfect and crude as their views on such points may be, yet they continued for more than a hundred years to be the foundation of all that was known about cellular structure; and when phytotomy took a new flight at the beginning of the present century, Malpighi's and Grew's scattered remarks on the union of cells with one another, and on the structure of fibres and vessels, were adopted by the later phytotomists and connected with their own investigations.

If the views of Malpighi and Grew agreed in the main on the points here mentioned, yet the style and manner of the two were very different. Malpighi kept more closely to that which could be directly seen; Grew delighted in tacking on a variety of theoretical discussions to his observations, and especially endeavoured to follow the path of speculation beyond the limits of what was visible with the microscope. Malpighi's account reads like a masterly sketch, Grew's like an elaborate production of great and almost pedantic carefulness; Malpighi displays a greater formal cultivation, and deals with the questions with light touches, allusively, and almost in the tone of conversation. Grew on the other hand is at pains to reduce the new science to a learned and well-studied system, and to bring it into connection with chemistry, physics, and above all with the Cartesian philosophy. Malpighi was one of the most famous physicians and zootomists of his time, and treated phytotomy from the points of view already opened in zootomy; Grew too occupied himself occasionally with zootomy, but he was a vegetable anatomist by profession, and gave himself up, especially after 1688, almost exclusively to the study of the structure of plants with a devotion hardly to be paralleled till we come down to Mirbel and von Mohl.

As in medicine in the 17th century human anatomy was intimately connected with physiology, and the latter was not yet treated as a distinct study, so the founders of phytotomy naturally combined the physiological consideration of the functions of organs with the examination of their structure. Considerations on the movement of sap and on food appear in the front of every anatomical enquiry; relations of structure, which the microscope could not reach, were assumed hypothetically on physiological grounds, although little positive was known at the time about the functions of the organs of plants; hence recourse was had to analogies between vegetable and animal life, and it is true that vegetable physiology received its first great impulse by this means, but occasion was given at the same time to many errors, which in their turn often misled the anatomist. At present, when vegetable anatomy has separated itself more than is desirable from physiology, that is, from the investigation of the functions of organs, it is difficult, nay impossible, to give the reader a brief account of the contents of these two books which form an epoch in the science. I must confine myself to noticing a few chief points, which are historically connected with the further development of phytotomy, though some of these are just the questions to which Malpighi and Grew only gave occasional attention, and which it is therefore a little unjust to them to bring into prominent notice. I shall recur to the physiological portion of their writings in the third book of this history, confining myself here to that which concerns the structural relations of plants.

The phytotomical work of Marcello Malpighi^[2] appeared under the title 'Anatome Plantarum,' and to it was added a treatise on hens' eggs during the process of incubation (1675). The phytotomical portion of the book separates into two main divisions, the first of which, the 'Anatomes Plantarum idea,' was, as was stated above, completed in 1671, and contains a general abstract and survey of Malpighi's views on the structure and functions of vegetable organs in fourteen-and-a-half folio pages; the second and much larger portion illustrates in detail by numerous examples and with the help of many copper-plates the views expressed in the first part; it will answer our purpose best to turn principally to the connected expression of the author's views in the first part. He begins his remarks with the anatomy of the stem, and as the rind first attracts the eye, he takes it first. The outer part of it, he says, the cuticle, consists of utricles or little sacs arranged in horizontal rows; these die in time and decay, sometimes forming a dry epidermis. On the removal of the epidermis, layer after layer of woody fibre is disclosed, and these layers, usually forming reticulations and lying one on another, follow the longitudinal direction of the stem. These fibrous bundles are composed of numerous fibres, and each single fibre of tubes which open into one another ('quaelibet fibra insignis fistulis invicem hiantibus constat') and so on. The interspaces of the network are filled with roundish tubes, which usually have a horizontal direction towards the wood. If the rind is removed the wood appears, chiefly composed of elongated fibres and tubes, and consisting of rings or vesicles open towards one another and arranged in longitudinal rows. The fibres also of the wood do not run parallel to one another, but allow a network of angular anastomosing spaces to be formed between them, the larger of which are filled with bundles of tubes, which run from the rind through these interspaces to the pith, etc., etc. Between the fibrous and fistulose bundles of the wood lie the spiral tubes ('spirales fistulae'), smaller in number but of larger size, so that in cross sections of the stem they appear with open orifices. They lie in different positions, but the majority in concentric circles. He says that in the course of ten years' examination (from 1661 therefore) he found these spiral tubes in all plants, and it may be added here that Grew in the introduction to his book expressly concedes the priority in this discovery to Malpighi; but Malpighi's ideas on the subject of these tubes are extremely indistinct^[3], and this gave occasion to much misinterpretation and to gross errors on the part of later writers. Malpighi thought he observed a peristaltic movement in these vessels, a delusion to which many of the nature-philosophers were particularly fond of surrendering themselves at the beginning of the present century.

In addition to the bundles of fibres and the tracheae, Malpighi observed a number of tubes in Ficus, Cupressus, and other plants, which allowed the escape of a milky juice, and he concludes that similar special tubes might be present also in the wood of stems from which milk, turpentine, gum, and the like exude.

Such are the elementary organs of plants, as far as they were known to Malpighi; in the subsequent part of his book we find them applied to a histology of the stem, and here a mistake at once makes its appearance, which, resting on his authority, was reproduced by the phytotomists of the 18th and even of the early part of the 19th century,—the theory, namely, that the young layers of wood in the stem originate in the periodic transformation of the innermost layers of bark (secondary bast-layers); Malpighi was led into this mistake, as it appears, partly by the softness and light colour of the alburnum, partly by its fibrous character. In this substance the spiral tubes are gradually formed, and as the mass becomes more solid and compact, it subsequently forms the true wood.

The pith lies in the centre of the stem, and, according to Malpighi, consists of numerous rows of spheres ('multiplici globulorum ordine') arranged longitudinally one after another, and composed of membranous tubes, as may be clearly seen in walnut, elder, and other trees. In this place also he mentions the milk-vessels in the pith of the elder. Passing over many and various matters, it may be mentioned next that Malpighi recognises the connection of the layers of tissue in young shoots with those of the parent-stem, and very expressly notices the same continuity of structure between the leaf and the axis of the shoot. He then briefly touches on the anatomical relations of the fruit and the seed, the existence of the embryo in the seed and its structure, and then goes on to the roots. 'The roots of trees are a part of the stem, which divides into branches and ultimately ends in capillary threads ('capillamenta'); so that, in fact, trees are simply fine tubes, which run separate from one another underground but gradually collect into bundles; these bundles unite further on with other and larger bundles, and all together ultimately join to form a single cylinder, the stem, which then by separation of the tubes at the opposite extremity stretches out its branches, and by continued gradual separation of the larger into smaller finally expands into leaves, and so reaches its furthest limits.' The conclusion of the whole account is chiefly concerned with the part played by the various kinds of tissue in the nourishment of the plant.

In the second part published in 1674, the different kinds of tissue in the stem are discussed at greater length; here there is much that is really good, but at the same time much that is imperfect to an extent which cannot be attributed solely to the inferiority of his microscope. Very excellent is the way in which he endeavours to make out the more obvious anatomical relations of the rind, the wood, and the pith, and in the texture of the rind and the wood connects the longitudinal course of the vessels and woody fibre with the horizontal course of the medullary rays and the 'silver-grain.' The magnifying powers which he used must, to judge from his figures, have been very considerable; how much of what is imperfect in them is due to the indistinctness of the field of view, and how much to inaccurate observation, we cannot say. For instance, he sees the bordered pits in the wood of Conifers without perceiving the central pore, and represents them as coarse grains lying on the outside of the wood-cells; it was unfortunate for Malpighi, as for his successors, that the large vessels in the wood of dicotyledons, to which they gave most of their attention, are often filled with secondary tissue ( thylosis), which Malpighi figures Tab. vi, fig. 21, but the true nature of which was not understood till 150 years later. Malpighi, like succeeding phytotomists till as late as 1830, lays great stress on the structure of the spiral vessels or tracheae, and mentions particularly that they are surrounded by a sheath of woody fibre; but he did not fall into the strange notions which Grew and other phytotomists entertained with regard to the nature of these vessels.

We may at present omit the numerous remarks on assimilation and the movement of the sap; the descriptions and figures of the parts of buds and of the course of the bundles of vessels in different parts of plants, and especially the analyses of the flower and fruit and the examination of the seed and embryo, conducted with a carefulness remarkable for that time, deserve a fuller notice, but this would detain us too long from our main subject.

If Malpighi's work reads like a masterly sketch in which the author is bent only on giving the outlines of the architecture of plants, the much more comprehensive work of Nehemiah Grew^[4], 'The anatomy of plantes' (1682), has the appearance of a text-book of the subject thoroughly worked out in all its details; the tasteful elegance of Malpighi is here replaced by a copiousness of minute detail that is often too diffuse; while in Malpighi we only occasionally encounter the philosophical prejudices of his time, which usually lead him into mistakes, Grew's treatise is everywhere interwoven with the philosophical and theological notions of the England of that day; but we are compensated for this by the more systematic way in which he pursues the train of thought, and especially by the constant effort to give as clear a representation as possible of what he sees. Though he too everywhere introduces physiological considerations into his anatomical investigation, yet he keeps himself free from many preconceptions which his successors imported in this way into phytotomy. To mention one point by anticipation, he avoided the erroneous notion so common at a later time, and first definitively removed by von Mohl in 1828, that the cell-walls must have visible openings to serve for the movement of the sap.

Grew's work, as has been said, separates into two main divisions; the first, 'The anatomy of plants begun, with a general account of vegetation founded thereupon,' was printed in 1671, and contains a brief and rapid account of the general anatomy and physiology of plants in forty-nine folio pages. Then the anatomy of roots, stems, leaves, flowers, fruits and seeds appeared as separate treatises in the following years up to 1682. We may pass over the chemical researches embodied in this work and the enquiries into the colours, taste and smell of plants, as well as the previously issued treatise, 'An idea of a philosophical history of plants,' which, as it was first laid before the Royal Society in 1672, we may imagine to have been intended as a counterpart to Malpighi's 'Anatomes plantarum idea,' though it is very different in character and admits much that is foreign to vegetable anatomy and physiology.

With Grew as with Malpighi the main point of enquiry is not the individual cell, but the histology; after distinguishing, like Malpighi, between the parenchymatous tissue and the longitudinally elongated fibrous forms, the true vessels and the sap-conducting canals, he is chiefly bent on explaining the combination of these tissues in the different organs of the plant; and in this point he is superior to Malpighi both in carefulness of description and in the beauty of his delineations. Grew's numerous figures on copper plates, more carefully executed than Malpighi's, give in fact so clear an idea especially of the structure of the root and stem that a beginner may still use them with advantage; such figures as those on plates 36 and 40 and elsewhere show that he knew how to fashion his observations by aid of much reflection into a clear representation of the thing seen; there are, as might be expected, many errors in the details of the more delicate structure of the various forms of vessels and cells.

Malpighi had not said, whether he considered the cells of the parenchyma (the term parenchyma comes from Grew) to be perfectly closed or porous, nor how they cohere; Grew leaves no doubt on this point; he says distinctly on page 61 that the cells or vesicles of the parenchyma are closed, that their walls are not traversed by any visible pores, so that the parenchyma may be compared to the foam of beer. He quotes Malpighi's view respecting the vessels of the wood, and supplements it by saying that the spiral band is not always single, but that two or more bands entirely separate from one another may form the wall of the vessel, and also that the spiral thread is not flat but roundish like a wire, and its turns are more or less close together according to the part of the plant. He also notices that the spiral tubes are never branched, and that when they run straight, as in Arundo Donax, they can be seen throughout considerable distances. The view of the structure of spiral vessels, which began with Malpighi and was maintained through the whole of the 18th century, Grew (p. 117) expresses still more distinctly than Malpighi; but it is to be observed that neither of them clearly distinguished true spiral vessels with separable spiral threads from vessels of the kind which occurs in secondary wood, and only shows a spiral structure on being torn. From the way, says Grew, in which the threads are woven, it comes to pass that the vessels often unroll into a flat surface, as we may imagine a narrow ribbon wound in a spiral about a round staff so that edge meets edge; and if the staff is drawn out, the ribbon so wound will remain behind in the form of a tube, and this would answer to an air-vessel in the plant. We should notice specially that Grew, better taught than the phytotomists of the 18th century, considers the vessels of the wood as air-passages, though they sometimes convey water. But he goes on with his description of the wall of the vessel; the flat surface disclosed by the unwinding of a vessel is, he says, itself composed of many parallel threads, as in an artificial ribbon, and the threads that are spirally wound answer to the warp in an artificial tissue, being held together by transverse threads, which correspond to the woof. To realise to ourselves this very strange idea of the structure of a spiral vessel as it appeared to Grew, we ought to know that he thinks that all cell-walls, even those of the parenchyma, are composed of an extremely fine web; his previous comparison of cell-tissue with foam was only intended to make the more obvious circumstances clear to the reader; his real idea is, that the substance of the walls of vessels and cells consists of an artificial web of the finest threads. He hints at this on pages 76 and 77, and on page 120 he returns once more to this conception and dwells upon it at great length. The most exact comparison, he says, which we can make of the whole body of a plant is with a piece of fine lace-tissue, such as women make upon a cushion; for the pith, the medullary rays, and the parenchyma of the rind are an extremely delicate and perfect tissue of thread. The threads of the pith run horizontally like the threads in a piece of woven stuff, and form the boundaries of the numerous vesicles of the pith and the rind, as the threads in a web bound the interstices in it. But the woody fibres and the air-vessels are perpendicular to this tissue, and therefore at right angles to the horizontal threads of the parenchyma, just as the needles in a piece of lace work that lies on the cushion are perpendicular to the threads. To complete the comparison we ought to suppose the needles to be hollow and the tissue of thread-lace in a thousand layers one above another. Grew himself states incidentally, that he lit upon this notion from looking at shrivelled masses of tissue, when he naturally saw wrinkles and folds, which he took for threads. Besides he seems to have used blunt knives, which might easily tear the cell-walls into threads; so we might gather from the figure in Plate 40, where what he supposes to have been a tissue of thread from the walls of a cell is depicted quite plainly. Lastly the observation of vessels with reticulated thickening, and parenchyma-cells with crossed striation may have contributed to his view.

It will hardly be superfluous to remark here, that Grew's idea of this very delicate structure of cell-walls has evidently given rise to the common expression cell-tissue (contextus cellulosus) when speaking of plants and animals, an expression which has become naturalised in microscopy, and is still retained though we no longer think of Grew's comparison of cell-structure with artificial lace. But the word tissue has often misled later writers, as words are apt to do, and made them found their conception of vegetable structure on the resemblance to an artificial tissue of membranes and threads.

Grew, like Malpighi, derives the young layers of wood in the stem from the innermost layers of the rind. The true wood, he says on page 114, is entirely composed of old lymph-vessels, that is of fibres, which lay originally in the inner circumference of the rind. But by true woody substance he understands the fibrous components of the wood, excluding the air-vessels; his lymph-vessels are the bast-fibres and similar forms; for, he goes on, the air-vessels with the medullary rays and the true wood form what is commonly called the wood of a tree; he uses the term air-vessels, not because these forms never contain sap, but because they only contain a vegetable air during the proper period of vegetation, when the vessels of the rind are filled with sap.

The above is certainly a very imperfect account of Grew's services to phytotomy; for the points here made prominent were treated by him as accessories only to the coarser histological relations with which he chiefly occupied himself.

These two works of Malpighi and Grew, so important not only for botany but for the whole range of natural science, were not followed during the course of the next hundred and twenty years by a single production, which can claim in any respect to be of equal rank with them; that long time was a period not of progress but of steady retrogression, as we shall see in the next chapter. But before the beginning of the 18th century Anton von Leeuwenhoek^[5] made some contributions to the knowledge of the details of vegetable anatomy, if not exactly to the settling of very important points in it; he communicated his observations on animal and vegetable anatomy in numerous letters to the Royal Society of London, and these appeared for the first time in a collected form in Delft in 1695 under the title of 'Arcana naturae.' It is not easy to gain a clear idea of Leeuwenhoek's phytotomic knowledge from his scattered statements. He too discussed the less minute anatomy of fruits, seeds and embryos, and among other things he made occasional observations on germination, and many on the structure of different woods. But all bears the stamp of only occasional study of plants; he was led to his observations by questions of the nature-philosophy then in vogue, and especially by such as were connected with the theory of evolution, not unfrequently by mere curiosity and pleasure in things obscure and inaccessible to ordinary people, but he did not gain from them a general idea of the structure of plants. In the course of these observations he did unquestionable service in perfecting simple magnifying glasses; he made a large number with his own hands, and these possessed magnifying powers evidently not at the command either of Malpighi or Grew. By aid of such glasses he discovered the vessels of secondary wood which are not spirally thickened but beset with pits, the true character of which however he did not investigate. He was the first moreover who perceived the crystals in vegetable tissue, namely in the rhizome of Iris florentina and in species of Smilax, and this could only be done with strong magnifying powers. In other matters he repeats the histological views of Malpighi and Grew, and on the whole his numerous communications seem painfully fragmentary and unscientific in presence of Malpighi's elegance and perspicuity, and Grew's systematic thoroughness. His figures too, which were not drawn by himself, are with some exceptions inferior to those of his great contemporaries.

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1. Robert Hooke, born in 1635 at Freshwater in the Isle of Wight, was a man of marvellous industry and varied acquirement in spite of a delicate constitution. He became a Fellow of the Royal Society in 1662, and was afterwards its Secretary and Professor of Geometry in Gresham College. He died in 1703. There is a good account of him by de l'Aulnaye in the 'Biographie Universelle.'
2. Marcello Malpighi, born at Crevalcuore near Bologna in 1628, became Doctor of Medicine in 1653, and after 1656 was Professor in Bologna, Pisa, Messina, and a second time in Bologna; in 1691 he was named Physician to Innocent XII. He died in 1694. On his services to comparative anatomy, and the anatomy of the human body, see the 'Biographie Universelle' and Carus, 'Geschichte der Zoologie,' p. 395.
3. We read at p. 3: 'Componuntur expositae fistulae (spirales) zona tenui et pellucida, velut argentei coloris, lamina parum lata, quae spiraliter locata et extremis lateribus unita tubum interius et exterius aliquantulum asperum efficit; quin et avulsa zona capites seu extreme trachearum tum plantarum tum insectorum non in tot disparates annulos resolvitur, ut in perfectorum trachea accidit; sed unica zona in longum soluta et extensa extrahitur.'
4. Nehemiah Grew, the son of a clergyman in Coventry, appears to have been born in 1628. Having taken a Doctor's degree in a foreign University, he practised as a physician in his native town, and pursued at the same time his phytotomical researches. He became Secretary to the Royal Society in 1677, and published his 'Cosmographia Sacra' in 1701. He died in 1711. See the 'Biographie Universelle.'
5. Leeuwenhoek's observations in animal anatomy were perhaps more important than those which he made in botany. Carus ('Geschichte der Zoologie,' p. 399) says of him: 'While Malpighi used the microscope with system and in accordance with the requirements of a series of investigations, the instrument in the hands of the other famous microscopist of the 17th century was more or less a means of gratifying the curiosity excited in susceptible minds by the wonders of a world which had hitherto been invisible. Still the discoveries, which were the fruit of an assiduous use of the microscope continued during fifty years, embraced many subjects and were important and influential. Anton von Leeuwenhoek was born in Delft in 1632. Being intended for trade, he had not the advantage of a learned education and is said even to have been ignorant of Latin; his favourite occupation was the preparing superior lenses, with which he incessantly examined new objects without being guided at any time by a scientific plan. The Royal Society of London, to whom he communicated his observations, made him a member of their body. He died in his native town in 1723, being ninety years of age.