Chapter IV: Introduction (3)

It is as a plant anatomist that Grew is chiefly famous, and it is important to try to realise exactly how far his conception of the anatomical structure of plants has been confirmed by more recent research. In appraising his work it must be remembered that he was essentially the pioneer of the science. It is true that some observations on plant anatomy occur in Robert Hooke's _Micrographia_, which was published six years before Grew sent in his first manuscript to the Royal Society; but Hooke never really attempted to make a systematic study of the subject. He had succeeded in greatly improving the microscope, and his chief interest was in applying his instrument to all kinds of bodies, vegetable and otherwise. Cork, charcoal, pith, etc., came under his observation, and to some extent he understood their structure. Grew acknowledges indebtedness to "the Learned and most Ingenious Naturalist M^r _Hook_," and tells us that some of the results which Hooke obtained, inspired him to study certain of his plants again with a better microscope. For instance Hooke was able to see smaller pores in wood than Grew had been able to detect, but, with better glasses, he confirmed the accuracy of Hooke's observation. However, although Hooke must certainly be credited with priority in the discovery of the fact that plant tissues are characterised by a cellular structure, his botanical work, considered in its entirety, is of very slight significance compared with that of Grew.

Grew's clearest account of plant cells is perhaps to be found in his description of root parenchyma, which he compares to "the Froth of _Beer_ or _Eggs_" or to "a fine piece of _Manchet_[11]," or again, to "a most curious and exquisitely fine-wrought Sponge." He quotes with approval Hooke's description of _Elder-Pith_ as "an heap of _Bubbles_." It would be unsafe however to conclude that he had really arrived at what is known as the Cell Theory. His conception of the nature of plant tissues was not by any means that of the modern botanist. He believed the cell-walls to consist of inter-woven fibres, which were continuous from cell to cell. He did not consider that these fibres were invariably wrought together in such a fashion as to enclose bladder-like spaces, or cells; in some cases he held that the tissue was non-cellular, consisting simply of interwoven fibres. It was these hypothetical fibres, rather than the cells, which he regarded as of fundamental importance. His idea, which is somewhat confusing, is perhaps best understood from his comparison of plant structure with pillow lace. The "most unfeigned and proper resemblance we can," he writes, "at present make of the whole _Body_ of a _Plant_, is, To a piece of _fine Bone-Lace_, when the Women are working it upon the _Cushion_, For the _Pith_, _Insertions_[12], and _Parenchyma_ of the _Barque_, are all extream Fine and Perfect _Lace-Work_: the _Fibres_ of the _Pith_ running _Horizontally_, as do the _Threds_ in a Piece of _Lace_; and bounding the several _Bladders_ of the _Pith_ and _Barque_, as the _Threds_ do the several _Holes_ of the _Lace_; and making up the _Insertions_ without _Bladders_, or with very small ones, as the same _Threds_ likewise do the _close_ Parts of the _Lace_, which they call the _Cloth-Work_. And lastly, both the _Lignous_ and _Aer-Vessels_, stand all _Perpendicular_, and so cross to the _Horizontal Fibres_ of all the said _Parenchymous Parts_; even as in a Piece of _Lace_ upon the _Cushion_, the _Pins_ do to the _Threds_. The _Pins_ being also conceived to be _Tubular_, and prolonged to any length; and the same _Lace-Work_ to be wrought many Thousands of times over and over again, to any thickness or hight, according to the hight of any _Plant_. And this is the true _Texture_ of a _Plant_."

Grew thus visualised the inner structure of the plant as a textile fabric, and the analogy between vegetable substance and woven threads seems to have been constantly present in his mind. The same idea also occurs, for instance, in the dedication of his _magnum opus_, where he says, "one who walks about with the meanest _Stick_, holds a Piece of Nature's Handicraft, which far surpasses the most elaborate _Woof_ or _Needle-Work_ in the World."

The notions at which Nehemiah Grew arrived on the subject of the vascular anatomy of plants were more advanced than his ideas on the ultimate nature of the tissues. There is no doubt that the comparison with animal anatomy, which was constantly in his mind, was on the whole helpful, though it led to some errors. The following paragraph, which occurs in the _Cosmologia Sacra_, seems to be an instance in which the analogy with the animal kingdom, helped him to take a broad view. "In the Woody Parts of Plants, which are their Bones; the Principles are so compounded, as to make them Flexible without Joynts, and also Elastick. That so their Roots may yield to Stones, and their Trunks to the Wind, or other force, with a power of Restitution. Whereas the Bones of Animals, being joynted, are made Inflexible."

In plants, as in animals, Grew looked for "vessels," and discovered by means of a simple experiment that continuous tubes, worthy of being called by this name, existed in the outer parts of the root, whereas the pith consisted of closed chambers. He cut a fresh root transversely, and then gently pressed the side of it with his finger nail. He was able to detect the vessels with the naked eye, and he observed that where they occurred, sap oozed out under pressure, but was sucked in again when the pressure was removed. The pressure also expressed a certain amount of sap from the pith, where vessels were absent, but here the sap was not sucked in again when the root was no longer squeezed, shewing that the liquid had only been forced out by the wounding of the cells. Had they been open tubes like the vessels, the release of the pressure would have caused the sap to disappear. Grew recognised that the vascular tissue of the root is centrally placed, whereas in the stem it is circumferential, and he points out that this difference is connected with the diverse mechanical needs of the two organs. It should also be noted that he discovered that concentration of the vascular system is characteristic of climbing plants, the wood, in his own words, standing "more close and round together in or near the Center, thereby making a round, and slender _Trunk_. To the end, it may be more tractable, to the power of the external _Motor_, what ever that may be: and also more secure from breaking by its winding _Motion_." He observed the radial arrangement of the xylem in the root, and offered an explanation of it, which is however scarcely free from obscurity. "Some of the more Æthereal and Subtile parts of the _Aer_, as they stream through the _Root_, it should seem, by a certain _Magnetisme_, do gradually dispose the _Aer-Vessels_, where there are any store of them, into _Rays_." Amongst other details of root anatomy, Grew discovered that all the tissues outside the central cylinder sometimes peel off when the root becomes old, or as he says, "the whole body of the Perpendicular _Roots_, except the woody _Fibre_ in the Centre, becomes the second _skin_." Turning to stem structure, we find that he understood the difference in origin between stem buds and adventitious roots. The stem bud, he writes, "carries along with it, some portion of every _Part_ in the _Trunk_ or _Stalk_; whereof it is a _Compendium_." The adventitious root, on the other hand, "always shoots forth, by making a Rupture in the _Barque_, which it leaves behind, and proceeds only from the inner part of the _Stalk_." He describes the vascular bundles of the stem as "fibres" perforated by numerous "pores." It would be a mistake, however, to suppose that he had no understanding of their structure, at least as regards the xylem, for he goes on to say that "each _Fibre_, though it seem to the bare eye to be but _one_, yet is, indeed, a great number of _Fibres_ together; and every _Pore_, being not meerly a space betwixt the several parts of the Wood, but the _Concave_ of a _Fiber_." He noticed the medullary rays, for which he uses the expressive term "Insertions." "These _Insertions_," he says, "are likewise very conspicuous in Sawing of _Trees_ length-ways into Boards, and those plain'd, and wrought into _Leaves_ for _Tables_, _Wainscot_, _Trenchers_, and the like. In all which, ... there are many parts which have a greater smoothness than the rest; and are so many _inserted Pieces_ of the _Cortical Body_; which being by those of the _Lignous_, frequently intercepted, seem to be discontinuous, although in the _Trunk_ they are really extended, in continued Plates, throughout its Breadth."

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 [is], 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[13]. 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[14] 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[15] 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 [he] 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_[16] 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:

[2] _Dict. Nat. Biog._, edited by Leslie Stephen and Sidney Lee, vol. XXIII. 1890.

[3] 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.

[4] 1701.

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

[6] 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].

[7] Aloys Pollender, _Wem gebührt die Priorität in der Anatomie der Pflanzen dem Grew oder dem Malpighi?_ Bonn, 1868.

[8] 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).

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

[10] By the courtesy of the Council of the Royal Society, I have been able to compare these annotations with certain manuscript letters of Nehemiah Grew's preserved in the Society's Library. This comparison confirms the view that the annotations are in Grew's own handwriting.

[11] Manchet = a loaf of fine wheaten bread. (_An Etymological Dictionary of the English Language._ W. W. Skeat. New ed. 1910.)

[12] Medullary rays.

[13] Ernst H. F. Meyer, _Geschichte der Botanik_, vol. IV. p. 60, 1857.

[14] M. Westermaier, "Zur Kenntniss der osmotischen Leistungen des lebenden Parenchym's." _Ber. d. deutsch. bot. Gesellsch._ Bd I. p. 371, 1883.

[15] _The Anatomy of Vegetables Begun_, 1672.

[16] Calyx.

STEPHEN HALES

1677-1761

BY FRANCIS DARWIN

An error corrected--Hales' scientific contemporaries--Physiology
or Physics--Hales the Founder of the experimental method in
Physiology--His style--Cambridge days--Teddington--_Vegetable
Staticks_--Experiments described--Transpiration--Root
Pressure--Assimilation--Practical application to
greenhouses--Distribution of growth first measured--Hales' other
activities--Sachs' tribute.

In attempting to give a picture of any man's life and work it is well to follow the rule of the _Dictionary of National Biography_, and begin with the dates of his birth and death. Stephen Hales was born in 1677 and died in 1761, having had experiences of the reigns of seven sovereigns.

The authorities for the life of Hales are given in my article on him in the _Dictionary of National Biography_. Botanists in general probably take their knowledge of the main facts of his life from Sachs' _History of Botany_. It is therefore worth while to point out that both the original and the English translation (1890) contain the incorrect statement that Hales was educated at Christ's College, Cambridge, and that he held the living of Riddington, whereas he is one of the glories of Corpus, and was perpetual curate of Teddington. These inaccuracies however are trifles in relation to the great and striking merits of Sachs' _History_, a work which to my thinking exhibits the strength and brilliance of the author's mind as clearly as any of his more technical writings. Sachs was no niggling biographer, and his broad vigorous outlines must form the basis of what anyone, who follows him, has to say about the Botanists of a past day.

To return to Hales' birth: it is of interest to note how he fits into the changing procession of lives, to see what great men overlap his youth, who were his contemporaries in his maturity, and who were appearing on the scientific stage as he was leaving it.

Sir Isaac Newton was the dominant figure in English science while Hales was developing. He died in 1727, the year in which Hales published his _Vegetable Staticks_, a book, which like the _Origin of Species_, appeared when its author was 50 years of age; Newton was at the zenith of his fame when Hales was a little boy of 10--his _Principia_ having been published in 1687. And when Hales went up to Cambridge in 1696 he must have seen the great man coming from his rooms[17] in the N.E. corner of the Great Court of Trinity--that corner where Newton's and other more modern ghosts surely walk--Macaulay who used to read, pacing to and fro by the chapel[18], and Thackeray who, like his own Esmond, lived "near to the famous Mr Newton's lodgings." In any case there can be no doubt that the genius of Newton cast its light on Hales, as Sachs has clearly pointed out (_Hist. Bot._, Eng. Tr., p. 477). Another great man who influenced Hales was Robert Boyle, who was born 1627 and died 1691. John Mayow again, that brilliant son of Oxford, whose premature death at 39 in 1679 was so heavy a blow to science, belongs to the same school as Hales--the school which was within an ace of founding a rational chemistry, but which was separated from the more obvious founders of that science by the phlogiston-theory of Becchers and Stahl. I do not find any evidence that Hales was influenced by the phlogistic writers and this is comprehensible enough, if, as I think, he belongs to the school of Mayow and Boyle.

The later discoverers in chemistry are of the following dates, Black 1728-1799, Cavendish 1731-1810, Priestley 1733-1804, Scheele 1742-1786, Lavoisier 1743, guillotined 1794. These were all born about the time of Hales' zenith, nor did he live[19] to see the great results they accomplished. But it should not be forgotten that Hales' chemical work made more easy the triumphant road they trod.

I have spoken of Hales in relation to chemists and physicists because, though essentially a physiologist, he seems to me to have been a chemist and physicist who turned his knowledge to the study of life, rather than a physiologist who had some chemical knowledge.

Whewell points out in his _History of the Inductive Sciences_[20] that the Physiologist asks questions of Nature in a sense differing from that of the Physicist. The _Why?_ of the Physicist meant _Through what causes?_ that of the Physiologist--To what end? This distinction no longer holds good, and if it is to be applied to Hales it is a test which shows him to be a physicist. For, as Sachs shows, though Hales was necessarily a teleologist in the theological sense, he always asked for purely mechanical explanations. He was the most unvitalistic of physiologists, and I think his explanations suffered from this cause. For instance, he seems to have held that to compare the effect of heat on a growing root to the action of the same cause on a thermometer[21] was a quite satisfactory proceeding. And there are many other passages in _Vegetable Staticks_ where one feels that his speculations are too heavy for his knowledge.

Something must be said of Hales' relation to his predecessors and successors in Botanical work. The most striking of his immediate predecessors were Malpighi 1628-1694, Grew 1628-1711, Ray 1627-1705, and Mariotte (birth unknown, died 1684); and of these the three first were born one hundred years before the publication of _Vegetable Staticks_. Malpighi and Grew were essentially plant-anatomists, though both dealt in physiological speculations. Their works were known to Hales, but they do not seem to have influenced him. We have seen that as a chemist Hales is somewhat of a solitary figure, standing between what may be called the periods of Boyle and of Cavendish. This is even more striking in his Botanical position, for here he stands in the solitude of all great original inquirers. We must go back to Van Helmont, 1577-1644, to find anyone comparable to him as an experimentalist. His successors have discovered much that was hidden from him, but consciously or unconsciously they have all learned from him the true method and spirit of physiological work.

It may be urged that in exalting Hales I am unfair to Malpighi. It may be fairer to follow Sachs in linking these great men together and to insist on the wonderful fact that before Malpighi's book in 1671, vegetable physiology was still where Aristotle left it, whereas 56 years later in 1727 we find in Hales' book an experimental science in the modern sense.

It should not be forgotten that students of animal physiology agree with botanists as to Hales' greatness. A writer in the _Encyclopædia Britannica_ speaks of him as "the true founder of the modern experimental method in physiology."

According to Sachs, Ray made some interesting observations on the transmission of water, but on the whole what he says on this subject is not important. There is no evidence that he influenced Hales.

Mariotte the physicist came to one physiological conclusion of great weight[22]; namely, that the different qualities of plants, e.g. taste, odour, etc., do not depend on the absorption from the soil of differently scented or flavoured principles, as the Aristotelians imagined, but on _specific differences_ in the way in which different plants deal with identical food material--an idea which is at the root of a sane physiological outlook. These views were published in 1679[23], and may have been known to Hales. He certainly was interested in such ideas, as is indicated by his attempts to give flavour to fruit by supplying them with medicated fluids. He probably did not expect success for he remarks, p. 360: "The specifick differences of vegetables, which are all sustained and grow from the same nourishment, is [_sic_] doubtless owing to the very different formation of their minute vessels, whereby an almost infinite variety of combinations of the common principles of vegetables is made." He continues in the following delightful passage: "And could our eyes attain to a sight of the admirable texture of the parts on which the specific differences in plants depends [_sic_] what an amazing and beautiful scene of inimitable embroidery should we behold? what a variety of masterly strokes of machinery? what evident marks of consummate wisdom should we be entertained with?" To conclude what has been said on Hales' chronological position--Ingenhousz, the chief founder of the modern point of view on plant nutrition, was born 1730 and published his book _On Vegetables_, etc. in 1779. So that what was said of Hales' chemical position is again true of him considered in relation to nutrition; he did not live to see the great discoveries made at the close of the 18th century.

There is in his writing a limpid truthfulness and simplicity, unconsciously decorated with pretty 18th century words and half-rusticities which give it a perennial charm. And inasmuch as I desire to represent Hales not merely as a man to be respected but also to be loved, it will be as well to give what is known of the personal side of his character before going on to a detailed account of his work.

He was, as we have seen, entered at Corpus Christi College, Cambridge, in June, 1696. In February, 1702-3, he was admitted a fellow of the College. It was during his life as a fellow that he began to work at chemistry in what he calls "the elaboratory in Trinity College." The room is now occupied by the Senior Bursar and forms part of the beautiful range of buildings in the bowling green, which, freed from stucco and other desecration, are made visible in their ancient guise by the piety of a son of Trinity and the wisdom of the College authorities. It was here, according to Dr Bentley, that "the thieving Bursars of the old set embezzled the College timber[24]," and it was this room that was fitted up as "an elegant laboratory" in 1706 for John Francis Vigani, an Italian chemist, who had taught unofficially in the University for some years and became the first Professor of Chemistry at Cambridge in 1703.

Judging from his book, _Medulla Chymiae_, 1682, Vigani was an eminently practical person who cared greatly about the proper make of a furnace and the form of a retort, but was not cumbered with theories.

Hales vacated his fellowship and became minister or perpetual curate of Teddington[25] in 1708-9 and there he lived until his death, fifty-two years afterwards. He was married (? 1719) and his wife died without issue in 1721.

He attracted the attention of Royalty, and received plants from the King's garden at Hampton Court. Frederick Prince of Wales, the father of George III, is said to have been fond of surprising him in his laboratory at Teddington. This must surely be a unique habit in a prince, but we may remember that, in the words of the Prince's mock epitaph, "since it is only Fred there's no more to be said." He became Clerk of the Closet to the Dowager Princess and this "mother of the best of Kings" as she calls herself put up his monument in Westminster Abbey. Hales had the honour of receiving the Copley Medal from the Royal Society in 1739, and Oxford made him a D.D. in 1733.

Some years ago I made a pilgrimage to Teddington and found, in the parish registers, many interesting entries by his hand; the last in a tremulous writing is on November 4th, 1760, two months before he died. He was clearly an active parish priest. He made his female parishioners do public penance when he thought they deserved it: he did much for the fabric of the church. "In 1754[26] he helped the parish to a decent water supply and characteristically records, in the parish register, that the outflow was such as to fill a two-quart vessel in 'three swings of a pendulum beating seconds, which pendulum was 39 + 2/10 inches long from the suspending nail to the middle of the plumbet or bob'." Under the tower he helped to build (which now serves as a porch) Stephen Hales is buried, and the stone which covers his body is being worn away by the feet of the faithful. By the piety of a few botanists a mural tablet, on which the epitaph is restored, has been placed near the grave.

Horace Walpole called Hales "a poor, good, primitive creature" and Pope[27] (who was his neighbour) said "I shall be very glad to see Dr Hales, and always love to see him, he is so worthy and good a man." Peter Collinson writes of "his constant serenity and cheerfulness of mind"; it is also recorded that "he could look even upon wicked men, and those who did him unkind offices, without any emotion of particular indignation; not from want of discernment or sensibility; but he used to consider them only like those experiments which, upon trial, he found could never be applied to any useful purpose, and which he therefore calmly and dispassionately laid aside."

Hales' work may be divided into three heads:

I. Physiological, animal and vegetable;
II. Chemical;
III. Inventions and miscellaneous essays.

Under No. I. I shall deal only with his work on plants. The last heading (No. III.) I shall only refer to slightly, but the variety and ingenuity of his miscellaneous publications is perhaps worth mention here as an indication of the quality of his mind. It seems to me to have had something in common with the versatile ingenuity of Erasmus Darwin and of his grandson Francis Galton. The miscellaneous work also exhibits Hales as a philanthropist, who cared passionately for bettering the health and comfort of his fellow creatures by improving their conditions of life.

His chief book from the physiological and chemical point of view is his _Vegetable Staticks_. It will be convenient to begin with the physiological part of this book, and refer to the chemistry later. _Vegetable Staticks_ is a small 8vo of 376 pages, dated on the title-page 1727. The "_Imprimatur_ Isaac Newton Pr. Reg. Soc." is dated February 16, 1726/7, and this date is of some slight interest, for Newton died on March 20, and _Vegetable Staticks_ must have been one of the last books he signed.

The dedication is to George Prince of Wales, afterwards George III. The author cannot quite avoid the style of his day, for instance: "And as _Solomon_ the greatest and wisest of men, deigned[28] to inquire into the nature of Plants, _from the Cedar of Lebanon, to the Hyssop that springeth out of the wall_. So it will not, I presume, be an unacceptable entertainment to your Royal Highness," etc.

But the real interest of the dedication is its clear statement of his views on the nutrition of plants. He asserts that plants obtain nourishment, not only from the earth, "but also more sublimed and exalted food from the air, that wonderful fluid, which is of such importance to the life of Vegetables and Animals," etc. We shall see that his later statement is not so definite, and it is well to rescue this downright assertion from oblivion.

His book begins with the research for which he is best known, namely that on transpiration. He took a sunflower growing in a flower-pot, covering the surface of the earth with a plate of thin milled lead, and cemented it so that no vapour could pass, leaving a corked hole to allow of the plant being watered. He did not take steps to prevent loss through the pot, but at the end of the experiment cut off the plant, cemented the stump and found that the "unglazed porous pot" perspired 2 ozs. in 12 hours, and for this he made due allowance.

The plant so prepared he proceeded to weigh at stated intervals. He obtained the area of the leaves by dividing them into parcels according to their several sizes and measuring one leaf[29] of each parcel. The loss of water in 12 hours converted to the metric system is 1·3 c.c. per 100 sq. cm. of leaf-surface; and this is of the same order of magnitude as Sachs' result[30], namely 2·2 c.c. per 100 sq. cm. He goes on to measure the surface of the roots[31] and to estimate the rate of absorption per area. The calculation is of no value, since he did not know how small a part of the roots is absorbent, nor how enormously the surface of that part is increased by the presence of root-hairs. He goes on to estimate the rate of the flow of water up the stem; this would be 34 cubic inches in 12 hours if the stem (which was one square inch in section) were a hollow tube. He then allowed a sunflower stem to wither and to become completely dry, and found that it had lost ¾ of its weight, and assuming that the ¼ of the "solid parts" left was useless for the transmission of water he increases his 34 by ⅓ and gives 45⅓ cubic inches in 12 hours as the rate. But the solid matter which he neglected contained the vessels and he would have been nearer to the truth had he corrected his figures on this basis. The simplest plan is to compare his results with those obtained by Sachs[32] in allowing plants to absorb solutions of lithium-salts. If the flow takes place through conduits equivalent to a quarter of a square inch in area, the fluid will rise in 12 hours to a height of 4 × 34 or 136 inches or in one hour to 28·3 cm.[33] This is a result comparable to, though very much smaller than, Sachs' result with the sunflower, viz. 63 cm. per hour.

The data are however hardly worth treating in this manner. But it is of historic interest to note that when Sachs was at work on his _Pflanzenphysiologie_, published in 1865, he was compelled to go back nearly 140 years to find any results with which he could compare his own.

We need not follow Hales into his comparison between the "perspiration" of the sunflower and that of a man, nor into his other transpiration experiments on the cabbage, vine, apple, etc. But one or two points must be noted. He found[34] the "middle rate of perspiration" of a sunflower in 12 hours of daylight to be 20 ounces, and that of a "dry warm night" about 3 ounces; thus the day transpiration was roughly seven times the nocturnal rate. This difference may be accounted for by the closure of the stomata at night.

Hales of course knew nothing of stomata, but it is surprising to find Sachs in 1865 discussing the problem of transpiration with hardly a reference to the effect of stomatal closure.

Hales[35] notes another point which a knowledge of stomatal behaviour might have explained, viz. that with "scanty watering the perspiration much abated," he does not attempt an explanation but merely refers to it as a "healthy latitude of perspiration in this Sunflower."

In the course of his work on sunflowers he notices that the flower follows the sun, he says however that it is "not by turning round with the sun," i.e. that it is not a twisting of the stalk, and goes on to call it _nutation_ which must be the _locus classicus_ for the term used in this sense.

An experiment[36] that I do not remember to have seen quoted elsewhere is worth describing. It is one of the many experiments that show the generous scale on which his work was planned. An apple bough five feet long was fixed to a vertical glass tube nine feet long. The tube being above and the branch hanging below the pressure of the column of water would act in concert with the suck of the transpiring leaves instead of in opposition to this force. He then cut the bare stem of his branch in two, placing the apical half of the specimen (bearing side branches and leaves) with its cut end in a glass vessel of water, the basal and leafless half of the branch remained attached to the vertical tube of water. In the next 30 hours only 6 ounces dripped through the leafless branch, whereas the leafy branch absorbed 18 ounces. This, as he says, shows the great power of perspiration. And though he does not pursue the experiment, it is worthy of note as an attempt like those of Janse[37] and others to correlate the flow of water under pressure with the flow due to transpiration.

It is interesting to find that Hales used the three methods of estimating transpiration which have been employed in modern times, namely, (i) weighing, (ii) a rough sort of potometer, (iii) enclosing a branch in a glass balloon and collecting the precipitated moisture, the well-known plan followed by various French observers.

He (_Vegetable Staticks_, p. 51) concluded his balance of loss and gain in transpiring plants by estimating the amount of available water in the soil to a depth of three feet, and calculating how long his sunflower would exist without watering. He further concludes (p. 57) that an annual rainfall (of 22 inches) is "sufficient for all the purposes of nature, in such flat countries as this about Teddington."

He constantly notes small points of interest, e.g. (p. 82) that with cut branches the water absorbed diminishes each day and that the former vigour of absorption may be partly renewed by cutting a fresh surface[38].

He also showed (p. 89) that the transpiration current can flow perfectly well from apex to base when the apical end is immersed in water.

These are familiar facts to us, but we should realise that it is to the industry and ingenuity of Hales that we owe them. In a repetition (p. 90) of the last experiment, we have the first mention of a fact fundamentally important. He took two branches (which with a clerical touch he calls _M_ and _N_) and having removed the bark from a part of the branch dipped the ends in water, _N_ with the great end downwards, but _M_ upside down. In this way he showed that the bark was not necessary for the absorption or transmission of water[39]. I suspect that one branch was inverted out of respect for the hypothesis of sap-circulation. He perhaps thought that water could travel apically by the wood, but only by the bark in the opposite direction.

Later in his book (pp. 128 and 131) he gives definite arguments against the hypothesis in question.

Next in order (p. 95) comes his well-known experiment on the pressure exerted by peas increasing in size as they imbibe water. There are, however, pitfalls in this result of which Hales was unaware, and perhaps the chief interest to us now is that he considered the imbibition of the peas[40] to be the same order of phenomenon as the absorption of water by a cut branch--notwithstanding the fact that he knew[41] the absorption to depend largely on the leaves. It may be noticed that Sachs with his imbibitional view of water-transport may be counted a follower of Hales.

In order to ascertain "whether there was any lateral communication of the sap and sap vessels, as there is of blood in animals," Hales (p. 121) made the experiment which has been repeated in modern laboratories[42], i.e. cutting a "gap to the pith" and another opposite to it and a few inches above. This he did on an oak branch six feet long whose basal end was placed in water. The branch continued to "perspire" for two days, but gave off only about half the amount of water transpired by a normal branch[43]. He does not trouble himself about this difference, being satisfied of "great quantities of liquor having passed laterally by the gap."

He is interested in the fact of lateral transmission in connexion with the experiment of the suspended tree (Fig. 24, p. 126), which is dependent on the neighbours to which it is grafted for its water supply. This seems to be one of the results that convinced him that there is a distribution of food material which cannot be described as circulation of sap in the sense that was then in vogue.

Hales (p. 143) was one of the first[44] to make the well-known experiment--the removal of a ring of bark, with the result that the edge of bark nearest the base of the branch swells and thickens in a characteristic manner. He points out that if a number of rings are made one above the other, the swelling is seen at the lower edge of each isolated piece of bark, and therefore (p. 143) the swelling must be attributed "to some other cause than the stoppage of the sap in its return downwards," because the first gap in the bark should be sufficient to check the whole of the flowing sap[45]. He must in fact have seen that there is a redistribution of plastic material in each section of bark.

We now for the moment leave the subject of transpiration and pass on to that of root-pressure on which Hales is equally illuminating.