Part 13

Nehemiah Grew was interested in the process of secondary thickening, but he only arrived at a dim notion of how it took place. He grasped, however, the important point that in a tree trunk the meristematic zone lies near the surface, "the young Vessels and Parenchymous Parts" being formed annually "betwixt the Wood and Barque." He describes how, "every year, the Barque of a Tree is divided into Two Parts, and distributed two contrary ways. The outer Part falleth off towards the Skin; and at length becomes the Skin it self.... The inmost portion of the Barque, is annually distributed and added to the Wood; the Parenchymous Part thereof making a new addition to the Insertions within the Wood; and the Lymphæducts a new addition to the Lignous pieces betwixt which the Insertions stand. So that a Ring of Lymphæducts in the Barque this year, will be a Ring of Wood the next; and so another Ring of Lymphæducts, and of Wood, successively, from year to year." Exactly what Grew meant by the term "Lymphæduct" is not always clear. In some cases he seems to refer to the phloem and cambium by this name, and in other cases to the perimedullary zone. The annual rings in Oak, Elm, Ash, etc. came under his observation, and he remarks that the difference between the Spring and Autumn wood, as we should now call it, arises from the fact that "the Aer-Vessels that stand in the inner margin of each annual Ring, are all vastly bigger, than any of those that stand in the outer part of the Ring."

From Grew's Anatomy

Sheweth the Parts of a Goosberry

Part of a Vine Branch cut transversly, and splitt half way downe y^e midle]

Grew did not enter into the minuter details of histology, except in his description of the spiral tracheids, to which, as we have seen, his attention was first called by Malpighi's observations. He speaks of the spiral as formed of "Two or More round and true Fibres, although standing collaterally together, yet perfectly distinct. Neither are these Single Fibres themselves flat, like a Zone; but of a round forme, like a most fine Thred." He makes the curious statement that the direction of the spiral is constant, being "in the Root, by South, from West to East: but in the Trunk, contrarily, by South, from East to West."

Although it is as an anatomist that Nehemiah Grew is best known, his grasp of external morphology is perhaps even more remarkable. His work on seed structure has already been quoted. He seems to have quite readily detected the true nature of modified stems. He examined for instance the thorns of the Hawthorn, and saw that their structure was axial. In his own words, they "are constituted of all the same substantial Parts whereof the Germen or Bud it self , and in a like proportion: which also in their Infancy are set with the resemblances of divers minute Leaves." It should be recalled that Albertus Magnus, the great scholastic philosopher, writing in the thirteenth century, distinguished between thorns and prickles, and noticed transitions between the former and leafy branches. There is no reason to suppose, however, that our author was acquainted with the work of Albertus. Grew realised the nature of Bulbs, and points out that "the Strings only, are absolute Roots; the Bulb, actually containing those Parts, which springing up, make the Leaves or Body; and is, as it were, a Great Bud under ground."

Nehemiah Grew was interested in plant physiology, although the state of chemical and physical knowledge at the time did not allow of his advancing so far in this, as in the morphological side of the subject. His turn of mind, too, appears to have naturally led him to the study of form rather than that of function. As regards the absorption of water, his idea was simply that the roots sucked up water like a sponge, because the parenchyma was of a spongy nature. He supposed that the liquid was rendered purer by being strained through the skin, which, according to whether it was of a texture resembling brown paper, cotton, or leather, would produce a different effect upon any solution passing through it. His explanation of the ascent of the sap had really much in common with the "Kletterbewegung" theory propounded by Westermaier almost exactly two hundred years later. Grew argued that "considering to what height and plenty, the Sap sometimes ascends; it is not intelligible, how it should thus ascend, by virtue of any one Part of a Plant, alone; that is neither by virtue of the Parenchyma, nor by virtue of the Vessels, alone." He pointed out that the parenchyma might suck up a liquid for a short distance, and also the vessels, like "small Glass-Pipes immersed in Water, will give it an ascent for some Inches; yet there is a certain period, according to the bore of the Pipe, beyond which it will not rise." To account for the rise he supposes that the vessels and parenchyma work together, the turgidity of the surrounding parenchyma cells both compressing the vessels, and thus causing the liquid in them to ascend, and also actually forcing some of their own contents into them. Grew performed a few experiments, especially in the direction of plant chemistry. This was a natural line of work for a doctor, since the extraction of various vegetable substances had long been practised in medicine. He noticed, amongst other points, that the green infusion obtained by treating a plant with olive oil would, at least in the case of certain aromatic plants, appear of a green colour in a small drop, but of a red, or deep yellow, when a quantity of it was held up against a candle. In other words, Grew seems to have observed the characteristic fluorescence of chlorophyll.

He was interested also in the subject of geotropism, and succeeded in proving that there is an innate tendency for the root to grow down and the stem to grow up; and that it is not merely a case of the root seeking the soil, and the stem the air. His directions for performing the experiment are as follows:--"Take a Box of Moulds, with a hole bored in the bottom, wide enough to admit the Stalk of a Plant, and set it upon stilts half a yard or more above ground. Then lodg in the Mould some Plant, for Example a Bean, in such sort, that the Root of the Bean standing in the Moulds may poynt upwards, the Stalk towards the ground. As the Plant grows, it will follow, that at length the Stalk will rise upward, and the Root on the contrary, arch it self downward. Which evidently shews, That it is not sufficient, that the Root hath Earth to shoot into, or that its Motion is only an Appetite of being therein lodged, which way soever that be: but that its nature is, though within the Earth already, yet to change its Position, and to move Downwards. And so likewise of the Trunk, that it rises, when a Seed sprouts, out of the Ground, not meerly because it hath an Appetite of being in the open Aer; for in this Experiment it is so already; yet now makes a new Motion upwards."

Although Grew cannot be called a great experimenter, he frequently took the easier course of throwing out suggestions for such work. "The generation of Experiments" he describes as "being like that of Discourse, where one thing introduceth an hundred more which otherwise would never have been thought of." Amongst other proposals he recommends that trial should be made of growing plants in common water, snow water, milk, oil, wine, ink, etc., or in any of these with solid bodies, such as nitre and salt, dissolved in them. He points out that the effect both on the plant and on the liquid should be noted. The solid body should be weighed before solution, and then, after the experiment is over, the liquid should be evaporated and the solid again weighed.

Another instance in which he suggested an experiment, apparently without carrying it out, was in relation to the movements of the stems of non-climbing plants. He seems to have anticipated the nineteenth century discovery of nutation amongst plants other than climbers, though he stopped short of actually proving it. In his account of the Motions of Trunks he remarks, "The Convolution of Plants, hath been observed only in those that Climb. But it seems probable, that many others do also wind; ... Whether it be so, or not the Experiment may easily be made by tying a Thred upon any of the Branches; setting down the respect it then hath to any Quarter in the Heavens: for, if it shall appear in two or three Months, to have changed its Situation towards some other Quarter; it is certain proof hereof." He noticed that some plants twine "by South from East to West" and others "from West to East," and attributed this to their being respectively under the influence of the sun and the moon.

Whenever Grew's notions of plant physiology depended upon chemistry, they became, according to our modern ideas, extremely difficult to follow. He held, among many other curious beliefs, that salts obtained from any plant have a tendency to crystallise out in a form resembling that plant, and adds, as an illustration from the animal world, "though I have not seen it my self, yet I have been told by one that doth not use to phancy things, that the Volatile Salt of Vipers, will figure it self into the semblance of little Vipers."

The mystical belief that characteristic "principles" permeate all things, finds expression in his idea that the "frost flowers," sometimes to be seen on a window pane, are evidence that the air is impregnated with "Vegetable Principles." Another fact, which he brings forward in support of the same view, is that the ground or water, when exposed for some time to air, turns green. His explanation, in this latter case, was not far from the truth, for, as we now know, the greenness is due to the vegetation of minute algæ, which, in their dormant state, may be carried from place to place by the wind.

It is usual to regard Ecology as a very recent development of botanical science, but Nehemiah Grew seems to have been alive to the importance of the ecological standpoint,--though he did not describe it by this name. He writes "The proper Places also of Plants, or such wherein they have ... a Spontaneous growth, should be considered. And that as to the Climate; whether in one Colder, Temperate, or more Hot. The Region; Continent, or Island. The Seat; as Sea, or Land, Watry, Boggy, or Dry; Hills, Plains, or Vallies; Open, in Woods, or under Hedges; against Walls, rooted in them, or on their Tops; and the like."

Grew's most interesting contribution to science was, perhaps, his publication of the fact that the flowering plants, like animals, shew the phenomena of sex. He never, however, actually proved this contention in an experimental way. At the time that his earliest work was published, he was frankly puzzled by the stamens, or, as he calls them, the "Attire." He recognised their use to insects, to whom flowers serve, in his own words, as "their Lodging and their Dining-Room." He also fully realised their value to man as increasing the beauty of the blossom, but he was broad-minded enough to feel that these must be secondary uses, and that "the primary and private use of the attire" remained to be discovered. Ten years later, in the second edition of his work, he tells us that it was suggested to him in conversation by Sir Thomas Millington that the stamens were the male organs. It seems probable that, although Grew gives Millington the credit for this discovery, he had really arrived at it independently, for he tells us that when Millington made the suggestion, he "immediately reply'd that was of the same Opinion; and gave him some reasons for it, and answered some Objections, which might oppose them."

Besides his belief in the male nature of the stamen, Nehemiah Grew came to some rather mysterious conclusions as to their serving to draw off the redundant part of the sap, not needed to produce the seed. He also used the word "attire" for the florets of the Compositæ, but qualified it by calling the stamens the "seminal attire," and the florets of compound flowers the "florid attire." He says that "every Flower with the Florid attire" (or, as we should now say, "every composite flower") "Embosomes, or is, a Posy of perfect Flowers." He recognised the "globulets" (pollen grains) as being of the same nature as those in the anthers of simple flowers. He describes the disk florets with remarkable accuracy, but falls into the error of supposing that the pollen grains are in some cases originally produced by the style and stigmas, which he calls the "Blade," and which he did not recognise as part of the female organ. His figures make it clear that he mistook the stylar hairs for little stalks organically connecting the pollen grains and the style. In other cases, however, he observed that the pollen grains occurred on the inner side of what we now know as the staminal tube.

Grew enters into considerable detail as regards the structure of flowers, and it is only possible to mention here a few of the points to which he draws attention. He observed the frequent occurrence of capitate glandular hairs, which he describes as "like so many little Mushrooms sprouting out of the Flower," their heads sometimes exuding a "Gummy or Balsamick Juyce." He describes the varieties of aestivation of the floral leaves, and notes that, in the Poppy, the large size and fewness of the petals prevents their being folded into a compact body by any of the ordinary methods. "For which reason, they are cramb'd up within the Empalement by hundreds of little Wrinckles or Puckers; as if Three or Four Fine Cambrick Handcherchifs were thrust into ones Pocket."

We have said something about Grew's work on seeds, in dealing with his first treatise. He was always much interested in this subject, and returned to it again in his later work. He mentions the mucilaginous testa possessed by many seeds, but which only becomes noticeable when they have been moistened. That of "Nasturtium Hortense" he describes as very large, "even emulous of the inner Pulp surrounding a Gooseberry-Seed." He suggests that the value of putting a Clary seed into the eye to bring out a foreign body, which may have lodged there, is due to the presence of the mucilaginous coat. The same seed is still, I believe, used for this purpose, under the name of "eye seed." Grew understood the difference between seeds with, and without endosperm, and gives perfectly clear representations of such albuminous seeds as Ricinus. He describes the cotyledons of the Dock as being immersed in the endosperm, "as in a Tub of Meal or a little pot of pure refin'd Mould, necessary for the first Vegetation of the Radicle."

Grew naturally reckoned the spores of Ferns among seeds. The seed-case of the Harts-tongue is, he says, "of a Silver Colour ... of a spherick Figure, and girded about with a sturdy Tendon or Spring, of the Colour of Gold: ... So soon as ... this Spring is become stark enough, it suddenly breaks the Case into two halfs, like two little cups, and so flings the Seed," of which "ten Thousand are not so big as a white Pepper Corn."

To give any kind of short summary of Grew's botanical work is well-nigh impossible. Some men are remembered for individual discoveries, and in such cases it is not difficult to give a précis of their contributions. But Nehemiah Grew is remembered because, contemporaneously with Malpighi, he actually created the science of plant anatomy,--a subject which, before his day, was practically non-existent. Modern botanists, conscious how small an addition to the fabric is now regarded as a satisfactory life-work, must stand amazed and somewhat humbled before the broad and sound foundations laid by this seventeenth century physician. It is no less than two hundred and forty years since Grew sent in his first treatise to the Royal Society, so it is scarcely wonderful that a number of his results have been rejected in course of time. It is far more remarkable that so many of his conclusions--and those the more essential ones--have been merely confirmed and extended by later work. Great however as were his actual contributions to botanical knowledge, they were perhaps less important than the far-reaching service which he rendered in helping to free biological thought from the cramping belief that the one and only object of the existence of the organic world was for the use and pleasure of man. Grew believed that the "Outward Elegancies of Plants" might be for the purpose of giving delight to the human race, but he was the first to point out that as the "Inward Ones, which, generally, are as Precise and Various as the Outward," are so seldom seen, their purpose can hardly be for this, but must be for the benefit of the plants themselves, "That the Corn might grow, so; and the Flower, so, whether or no Men had a mind, leisure, or ability, to understand how."

FOOTNOTES:

Dict. Nat. Biog., edited by Leslie Stephen and Sidney Lee, vol. XXIII. 1890.

Enoch's Translation. A Funeral Sermon Upon the Sudden Death of Dr Nehemiah Grew, Fellow of the College of Physicians. Who died March 25th, 1712. Preach'd at Old-Jewry. By John Shower. London. 1712.

1701.

Life of Robert Boyle by Thomas Birch, p. 83, 1744.

M. J. Schleiden, Grundzüge der wissenschaftlichen Botanik, Vol. I. p. 198, 1842. The incorrect statement that Grew was Secretary of the Royal Society at the time that Malpighi's manuscript was received by that body, is also repeated in the English translation of Schleiden's work [Schleiden's Principles of Scientific Botany, translated by Edwin Lankester, London, 1849, p. 38].

Aloys Pollender, Wem gebührt die Priorität in der Anatomie der Pflanzen dem Grew oder dem Malpighi? Bonn, 1868.

Marcellus Malpighi, Anatome Plantarum, 2 pts, London, 1875 and 1879 (see also Marcellus Malpighi, Die Anatomie der Pflanzen, Bearbeitet von M. Möbius, Leipzig, 1901. In this little book the more important parts of Malpighi's work are translated into German, and a number of the figures reproduced).

The order of the paragraphs cited is slightly altered from that of the original.