Part 9

He goes on to measure the surface of the roots {126b} 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 .75 of its weight, and assuming that the .25 of the "solid parts" left was useless for the transmission of water he increases his 34 by 1/3 and gives 45-1/3 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 {126c} 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. {126d} 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 {127a} 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, a phenomenon unknown to Hales.

Hales {127b} 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 {128a} that I do not remember to have seen quoted elsewhere is worth describing. It is incidentally of interest as showing 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 {128b} 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. {129a}

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. {129b} 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.

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 {130a} to be the same order of phenomenon as the absorption of water by a cut branch--notwithstanding the fact that he knew the absorption to depend largely on the leaves. {130b} It may be noticed that Sachs, in 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, {130c} _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. {130d} 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 {131a} 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. {131b} 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.

His first experiment (_Vegetable Staticks_, p. 100), was with a vine, to which he attached a vertical pipe made of three lengths of glass-tubing jointed together. His method is worth notice. He attached the stump to the manometer with a "stiff cement made of melted Beeswax and Turpentine, and bound it over with several folds of wet bladder and pack-thread." We cannot wonder that the making of water-tight connexions was a great difficulty, and we can sympathise with his belief that he could have got a column more than 21 feet high but for the leaking of the joints on several occasions. He notes the familiar fact that the vine-stump absorbed water before it began to extrude it.

He afterwards (pp. 106-7) used a mercury gauge, and registered a root-pressure of 32.5 inches or 36 feet 5.5 inches of water, which he proceeds to compare with his own determination of the blood-pressure of the horse (8 feet) and of other animals. Perhaps the most interesting of his root-pressure experiments was that (p. 110) in which several manometers were attached to the branches of a bleeding vine, and showed a result which convinced him that "the force is not from the root only, but must proceed from some power in the stem and branches," a conclusion which some modern workers have also arrived at.

Assimilation.

Hales' belief that plants draw part of their food from the air, and again, that air is the breath of life, of vegetables as well as of animals (p. 148), are based upon a series of chemical experiments performed by himself. Not being satisfied with what he knew of the relation between "air" (by which he meant gas) and the solid bodies in which he supposed gases to be fixed, he delayed the publication of _Vegetable Staticks_ for some two years, and carried out the series of observations which are mentioned in his title-page as "An attempt to analyse the air, by a great variety of chymio-statical experiments," occupying 162 pages of his book. {133}

The theme of his inquiry he takes (_Vegetable Staticks_, p. 165) from "the illustrious Sir _Isaac Newton_," who believed that "dense bodies by fermentation rarify into several sorts of Air; and this Air by fermentation, and sometimes without it, returns into dense bodies."

Hales' method consisted in heating a variety of substances, _e.g._ wheat-grains, pease, wood, hog's blood, fallow-deer's horn, oyster-shells, red-lead, gold, etc., and measuring the "air" given off from them. He also tried the effect of acid on iron filings, oyster-shells, etc. In the true spirit of experiment he began by strongly heating his retorts (one of which was a musket barrel) to make sure that no air arose from them. It is not evident to me why he continued at this subject so long. He had no means of distinguishing one gas from another, and almost the only quality noted is a want of permanence, _e.g._ when the CO2 produced was dissolved by the water over which he collected it. Sir E. Thorpe {134a} points out that Hales must have prepared hydrogen, carbonic acid, carbonic oxide, sulphur dioxide, and marsh gas. It may, I think, be said that Hales deserved the title usually given to Priestley, viz. "the father of pneumatic {134b} chemistry."

Perhaps the most interesting experiment made by Hales is the heating of minium (red-lead) with the production of oxygen. It proves that he knew, as Boyle, Hooke and Mayow did before him, that a body gains weight in oxidation. Thus Hales remarks: "That the sulphurous and aereal particles of the fire are lodged in many of those bodies which it acts upon, and thereby considerably augments their weight, is very evident in Minium or Red Lead, which is observed to increase in weight in undergoing the

## action of the fire. The acquired redness of the Minium indicating the

addition of plenty of sulphur in the operation." He also speaks of the gas distilled from minium, and remarks: "It was doubtless this quantity of air in the Minium which burst the hermetically sealed glasses of the excellent _Mr. Boyle_, when he heated the Minium contained in them by a burning glass" (p. 287).

This was the method also used by Priestley in his celebrated experiment of heating red-lead in hydrogen, whereby the metallic lead reappears and the hydrogen disappears by combining with the oxygen set free. This was expressed in the language of the day as the reconstruction of metallic lead by the addition of phlogiston (the hydrogen) to the calx of lead (minium). Thorpe points out the magnitude of the discovery that Priestley missed, and it may be said that Hales too was on the track, and had he known as much as Priestley it would not have been phlogiston that kept him from becoming a Cavendish or Lavoisier. What chiefly concerns us, however, is the bearing of Hales' chemical work on his theories of nutrition. He concludes that "air makes a very considerable part of the substance of Vegetables," and goes on to say (p. 211) that "many of these

## particles of air" are "in a fixt state, strongly adhering to and wrought

into the substance of" plants. {135a} He has some idea of the instability of complex substances, and of the importance of the fact, for he says {135b} that "if all the parts of matter were only endued with a strongly attracting power, [the] whole [of] nature would then become one unactive cohering lump." This may remind us of Herbert Spencer's words: "Thus the essential characteristic of living organic matter, is that it unites this large quantity of contained motion with a degree of cohesion that permits temporary fixity of arrangement" (_First Principles_, section 103). With regard to the way in which plants absorb and fix the "air" which he finds in their tissues, Hales is not clear; he does not in any way distinguish between respiration and assimilation. But as I have already said, he definitely asserts that plants draw "sublimed and exalted food" from the air.

As regards the action of light on plants, he suggests (p. 327) that "by freely entering the expanded surfaces of leaves and flowers" light may "contribute much to the ennobling principles of vegetation." He goes on to quote Newton (_Opticks, query_ 30): "The change of bodies into light, and of light into bodies, is very conformable to the course of nature, which seems delighted with transformations." It is a problem for the antiquary to determine, whether or no Swift took from Newton the idea of bottling and recapturing sunshine as practised by the philosopher of Lagado. He could hardly have got it from Hales, since _Gulliver's Travels_ was published in 1726, before _Vegetable Staticks_.

Nevertheless, Hales is not quite consistent about the action of light; thus (p. 351) he speaks of the dull light in a closely planted wood as checking the perspiration of the lower branches, so that "drawing little nourishment, they perish." This is doubtless one effect of bad illumination under the above-named conditions, but the check to photosynthesis is a more serious result. In his final remarks on vegetation (p. 375) Hales says in relation to green-houses, "It is certainly of as great importance to the life of the plants to discharge that infected rancid air by the admission of fresh, as it is to defend them from the extream cold of the outward air." This idea of ventilating greenhouses he carried out in a plant-house designed by him for the Dowager Princess of Wales, in which warm fresh air was admitted. The house in question was built in 1761 in the Princess's garden at Kew, which afterwards became what we now know as Kew Gardens. The site of Hales' greenhouse, which was only pulled down in 1861, is marked by a big wistaria which formerly grew on the greenhouse wall. It should be recorded that Sir W. Thiselton-Dyer {137a} planned a similar arrangement independently of Hales, and found it produced a marked improvement of the well-being of the plants.

It is worthy of note, that though Hales must have known Malpighi's theory of the function of leaves (which was broadly speaking the same as his own), he does not as far as I know refer to it. In his preface (p. ii.) he regrets that Malpighi and Grew, whose anatomical knowledge he appreciated, had not "fortuned to have fallen into this statical {137b} way of inquiry." I believe he means an inquiry of an experimental nature, and I think it was because Malpighi's theory was dependent on analogy rather than on ascertained facts that it influenced Hales so little.

There is another part of physiology on which Hales threw light. He was the first, I believe, to investigate the distribution of growth in developing shoots and growing leaves, by marking them and measuring the distance between the marks after an interval of time. He describes (p. 330) and figures (p. 344) with his usual thoroughness the apparatus employed; this was a comb-like object made by fixing into a handle five pins .25 inch apart from one another; the points being dipped in red-lead and oil, a young vine-shoot was marked with ten dots .25 inch apart. In the autumn he examined his specimen, and finds that the youngest internode or "joynt" had grown most, and the basal part having been "almost hardened" when he marked it, had "extended very little." In this--a tentative experiment--he made the mistake of not re-measuring his plants at short intervals of time, but it was an admirable beginning, and the direct ancestor of Sachs' {138a} great research on the subject. In his discussion on growth it is interesting to find the idea of turgescence supplying the motive force for extension. This conception he takes from Borelli. {138b}

Hales sees in the nodes of plants "plinths or abutments for the dilating pith to exert its force on" (p. 335); but he acutely foresees a modern objection {138c} to the explanation of growth as regulated solely by the hydrostatic pressure in the cell. Hales says (p. 335): "But a dilating spongy substance, by equally expanding itself every way, would not produce an oblong shoot but rather a globose one."

It is not my place to speak of Hales' work in animal physiology, nor of those researches bearing on the welfare of the human race which occupied his later years. Thus he wrote against the habit of drinking spirits, and made experiments on ventilation by which he benefited English and French prisons, and even the House of Commons; then too he was occupied in attempts to improve the method of distilling potable water at sea, and of preserving meat and biscuit on long voyages. {139a}

We are concerned with him simply as a vegetable physiologist, and in that character his fame is imperishable. Of the book which I have been using as my text, namely, _Vegetable Staticks_, Sachs says: "It was the first comprehensive work the world had seen which was devoted to the nutrition of plants and the movement of their sap. . . . Hales had the art of making plants reveal themselves. By experiments carefully planned and cunningly carried out he forced them to betray the energies hidden in their apparently inactive bodies." {139b} These words, spoken by a great physiologist of our day, form a fitting tribute to one who is justly described as the father of physiology.

IX NULLIUS IN VERBA {140}

There is a well-known story of Charles Darwin which I shall venture to repeat, because nothing can better emphasise the contrast between Shrewsbury School as it is and as it was.

Charles Darwin used, as a boy, to work at chemistry in a rough laboratory fitted up in the tool-house at his home in Shrewsbury. The fact that he did so became known to his school-fellows, and he was nicknamed "Gas." I have an old Delphine Virgil of my father's in which this word is scrawled, together with the name Miss Case, no doubt a sneer at his having come from Case's preparatory school. Dr. Butler, the Head Master, heard of the chemical work, and Charles Darwin was once publicly rebuked by that alarming person for wasting his time on such useless subjects. My father adds, "He called me very unjustly a _poco curante_, and as I did not understand what he meant it seemed to me a fearful reproach." A _poco curante_ means of course "a don't-care person" or one who takes no interest in things, and might perhaps be translated by "slacker." I do not suppose that Dr. Butler is likely ever to be forgotten, but as it is, he is sure of a reasonable share of immortality as the author of a description so magnificently inappropriate. {141a}

This is the contrast I referred to; on one hand a Head Master in 1822 doing his best to discourage a boy from acquiring knowledge of a great subject in the best possible way, _i.e._ by experiment. And on the other, a Head Master of the same school in 1911 encouraging, with a wise zeal, the rational study of science as a regular part of the school course. It may not be possible to trace out the complete evolution of these Darwin Buildings, but I like to fancy that the germ from which they have sprung is that tool house at the Mount. {141b}

It is some comfort to us to know that Shrewsbury was not the only place which failed to educate my father in the regulation lines. When he left school he went to Edinburgh University to study medicine. But he found anatomy and _materia medica_ intolerable, and the operating theatre was a horror. So he began to work at science in his own way. He learned to stuff birds from an old negro who had known Waterton. Of this instructor he says, "I used often to sit with him, for he was a very pleasant and intelligent man." He also caught sea beasts in the pools on the shore, and made one or two small observations, which were communicated to the Plinian Society.

Then he was sent to Cambridge with a view to taking Orders. He enjoyed himself riding and shooting, and especially in catching beetles in the fens. But also in more intellectual ways, as in listening to the anthem in King's Chapel, and looking at the pictures in the Fitzwilliam Museum. Henslow, the Professor of Botany treated him as a friend rather than as a pupil, and finally settled his career by sending him round the world in H.M.S. _Beagle_. He entered the ship an undergraduate, and left it after five years a man of science. I give these well known details to show how little he profited by any regular course of study either at Shrewsbury, Edinburgh, or Cambridge. His start in life depended on the recognition of his capacity by Henslow, and was nearly wrecked by FitzRoy, the Captain of the _Beagle_, suspecting that no one with a nose like my father's could be an energetic person.