Part 24

Later on in the same year (1809) he read a masterly paper on the Asclepiadaceae which was subsequently printed in the Memoirs of the Wernerian Natural History Society. This Natural Order was here separated by him from the Apocynaceae, from which it had not previously been distinguished, and a correct account of the relations of the remarkable androecium, so characteristic of the Asclepiad flower, was given. Twenty-two years later (in 1831) he again returned to the Asclepiads and described and discussed the mode of pollination and fertilisation in this Order and also in that of the Orchids.

It was characteristic of Brown that he clung with great tenacity to any problem that had once excited his interest. He made himself fully acquainted with the work of his contemporaries and predecessors, and at the same time he constantly attacked it by reiterated first-hand investigations, testing hypotheses and theories by the light of direct observation. He was very cautious, and thus, although he traced the pollen tubes from the pollen grain into the ovary and into the micropyle (foramen) of the ovule, he still leaves it an open question whether, in all cases, anything of a material nature passes from the pollen to the interior of the ovule, which may thus be held responsible for the formation of an embryo.

He cites the observations of Amici and of Du Petit Thouars, and then states he does not feel he is as far advanced as these observers. But in the succeeding pages he traces the tube, of which he says, "the production is a vital action excited in the grain by the application of an external stimulus." We see here a clear perception of the facts of germination and of the operation of what we now call chemiotaxis, for he goes on to add "The appropriate and most powerful stimulus to this action is no doubt contact, at the proper period, with the secretion or surface of the stigma of the same species. Many facts, however, and among others the existence of hybrid plants, prove that this is not the only stimulus capable of producing the effect; and in Orchideae I have found that the action in the pollen of one species may be excited by the stigma of another belonging to a very different tribe." It is hard to believe that these lines were written so long as 80 years ago. Brown goes on to describe the change that follows impregnation, and the gradual appearance of the embryo. And we must remember that all these observations were made by one who relied almost exclusively on the simple microscope and the simplest--I had almost said barbaric--technique.

He expresses himself in very reserved terms as to the nature of the "immediate agent derived from the male organ, or the manner of its application to the ovulum in the production of that series of changes constituting fecundation." But he puts forward the opinion that a more attentive examination of the process in Orchids and Asclepiads is more likely to be fruitful of results than most other families.

He returns again to this matter of fecundation in the following year, studying several orchids, but especially Bonatea, for the purpose. He is somewhat shaken as to the validity of his former inferences, and concludes that the "mucous cords" (i.e. strings of pollen tubes) are perhaps derived from pollen "not, however, by mere elongation of the original pollen tubes, but by an increase in their number, in a manner which I do not attempt to explain." In this later paper he also hazards the suggestion that in Ophrys, as impregnation is frequently accomplished without the aid of insects, "... it may be conjectured that the remarkable forms of the flowers in this genus are intended to deter, not to attract, insects." Also he suggests that the insect forms in orchidaceous flowers resemble those of the insects belonging to the native country of the plants. This is a clear foreshadowing of what is now called protective mimicry--and the former suggestion is not at any rate wholly without modern supporters, though Brown's share in its origin seems not to be generally recognised.

The keen desire to get to the bottom of a problem, which was so outstanding a feature of Brown's whole mental attitude, unquestionably explains why he was led to make so many important discoveries in such widely different directions. His first hand knowledge of the structure of a vast number of plants gave a soundness and depth to his morphological investigations that must arouse the admiration of everyone who is acquainted with them. He was never satisfied with perfunctory attempts to solve a problem, but, as we have already seen, in the example of his studies on Asclepiads and Orchids, he would return again and again to the matter till he had satisfied himself of the accuracy of his work. It is a pity that all of the present day botanists do not follow more closely in his steps in this respect. Publication of a paper seems to some to be a matter of greater importance than the advance of knowledge by the scientific and scholarly solution of a problem. Such was not Brown's view, and he practised wise delay in publication--nonumque prematur in annum, a maxim so strongly advocated by the Latin poet, was really put into practice by him as it also was by some of his contemporaries. Dryander, Solander and others have left, as Brown has done, rich stores of MS. behind them, which have never passed through the press.

The habit of long and continuous reflection on fundamental problems, which was so marked a feature of Brown's character, was perhaps responsible for the curious manner in which some of his most valuable and suggestive contributions to science, and especially to morphology, were given to the world, a habit to which I have already adverted.

We know he had been for many years interested in the ovule, and he made a number of important discoveries respecting it. Closely bound up with this topic were his studies on the Cycads and Conifers. He observed the plurality of embryos in the seeds of these plants, and, indeed, makes a reference to the phenomenon of polyembryony in the Prodromus, in which, as in most of his systematic works, morphological observations of the highest value are scattered, though embodied in very compressed phrases, amongst the descriptions of species. But every now and then when writing on one subject he seems to be carried away with the rush of his ideas on general questions. Thus in a memoir on the genus Kingia he entitles the paper, possibly to save his face after he had written it, "Character and Description of Kingia; a new genus of plants found on the south-west coast of New Holland. With observations on the Structure of its unimpregnated Ovulum, and on the female flower of Cycadeae and Coniferae."

This paper is, perhaps, one of the most important of his works, for it was there that, having briefly dismissed the genus Kingia, he "let himself go" on the ovule, and then in a masterly dissertation, puts forward his view on the gymnospermic nature of the Cycads and Conifers.

He summarises what was known at that time as to the structure of the ovule, acutely criticising the views of the various authors he cites. He emphasises the need of studying the development in order successfully to interpret the mature structure. He insists on the origin of the seed coats from the integuments, on the orientation of the embryo within the amnios (embryo sac), and on the distinction between the true albumen which is contained in this "amnios" and the albumen "formed by a deposition of granular matter in the cells of the nucleus" (nucellus), i.e. the perisperm, and he goes on to suggest that in some of these cases the "Membrane of the amnios seems to be persistent, forming even in the ripe seed a proper coat for the embryo.... This is the probable explanation of the structure of true Nympheaceae" ... here he seems to have overlooked the rudimentary endosperm which is really present. Finally he sums up an admirable account of the whole matter as follows:--"The albumen, properly so-called, may be formed either by a disposition or secretion of granular matter in the utriculi of the amnios, or in those of the nucleus itself, or lastly that two substances having these distinct origins and very different textures may coexist in the ripe seed as is probably the case in Scitamineae."

He then goes on at once to argue that the apex of the nucleus is the point of the ovulum where impregnation takes place, and adds that "all doubt would be removed if cases could be produced where the ovarium was either altogether wanting or so imperfectly formed that the ovulum itself became directly exposed to the action of the pollen or its fovilla." This leads him at once to enunciate his view of the gymnospermy of Cycads, Conifers and Gnetaceae. He reviews very fully the opinions that had been expressed by others as to the real structure of the female organ, especially of Pinus, and he mentions the fact that he himself in the botany of the Flinders' voyage had previously held the view that a minute perianth was present in the Pine, a view which, as he says, "On reconsidering the subject in connection with what I had ascertained respecting the vegetable ovulum" he had now abandoned.

The morphology of the male sporophyll of Cycas, however, presents a great difficulty, and Brown, less fortunate here, discusses a number of what seemed to him possible explanations. The recognition of Sporangia was remote, and the effort to homologise the numerous pollen sacs either to grains of pollen which, bursting, liberated fovilla, or to male flowers, or to explain them in other ways, was not very successful. The fact is this was a piece of morphology for which the age was not ready. We must recollect that the comparative morphology of the ovule (in the wide sense) was not attempted. Brown's main contribution to the understanding of this structure consisted in the empirical accuracy with which he elucidated the actual structure--he made no attempt to frame a comparative morphology, for the simple reason that in the condition of knowledge at the time no such comparative morphology was possible or even dreamed of.

Two other remarkable discoveries now demand our attention, and both are instructive as shewing the keenness with which his highly trained powers of observation followed up the clues which his brilliant intellect had enabled him to descry. It was while engaged on a study of the Orchids and Asclepiads that he was led to recognise the existence of the cell nucleus. He worked almost exclusively with what we should call a dissecting microscope. One of his instruments is preserved in the Natural History Museum, and it is well to examine it and reflect on how much may be discerned even with a very primitive instrument if only a good brain lies behind the retina. The "microscope" contains a number of simple lenses of various powers, the highest about 1/32" F.L. It is easy with such an instrument to see the nucleus in the epidermal cells when one knows it is there, but to have discovered it, and at a time when the technique of staining, &c., was simply non-existent, was a triumph of genius. Brown, of course, could not fully appreciate the great importance of his discovery, but he quite realised that he was dealing with no isolated or trivial fact, and, with characteristic industry and enterprise, he searched many other plants to find out whether his newly recognised nucleus was general or not; he found it to be so, and we all know how the discovery began at once to bear fruit.

A second observation to which I would refer was also of wide interest, and it was not made merely by chance. Brown was anxious to penetrate if possible into the secrets of fertilisation. He seems to have been pretty sure that something more than the mere "aura" of older writers was concerned in the matter, and while looking into the evidence for the existence or transmission of material substance, he observed that in the fovilla of the pollen there were vast crowds of minute particles which were in a continual state of dancing motion. He hoped that it might be possible to identify these bodies along their track into the ovule, and so to settle the more urgent questions as to the mode of fertilisation. He states that he made his observations with a simple microscope, the focal length of the lens of which was 1/32". Later on he used a much more powerful pocket microscope made by Dollond with power up to 1/70" F.L. He got Dollond to check the results with a compound achromatic microscope, and estimated the size of the particles to be 1/20,000 to 1/30,000". Brown was fully aware that he was not the first observer who had seen these moving particles. They had been already noticed by Needham and by Gleichen, but these writers had paid no special attention to them. Brown's great merit in this matter lies in the admirable way in which he conducted the investigation. At first he thought he had lighted upon something which was essentially a peculiarity of the male elements; then, extending his observations, he had to expand his first idea and admit the "active molecules" to represent a state or condition of living matter generally. As he still further widened the sphere of his investigations, he proved that the same movements occurred in dead tissues, and further that inorganic bodies also exhibited the phenomenon. Later on he found that the movements depended on the minuteness of the particles. He excluded the effect of evaporation, currents and other disturbing influences, and, indeed, the whole investigation shews him to us in the character of an accomplished experimenter as well as a brilliant observer. The complete explanation of these "active molecules," which are in the state generally described as "Brownian movement," still constitutes an unsolved problem, and one finds that it even now continues to occupy the attention of the physicist.

Any attempt adequately to review the whole of Brown's life work is impossible within the limits necessarily imposed by the conditions of a lecture, and I make no pretence to completeness, but will endeavour rather to indicate what appear to be the more important of his many other contributions to science.

His catalogues of the plants collected by those associated with various expeditions, his Kew lists (which were published under Aiton's name) are well known to students of systematic Botany, but his fine monograph on Rafflesia, containing, as it does, many observations of general interest will well repay perusal even after these many years. His studies on Cephalotus, on Caulophyllum (with its remarkable seed formation), as well as his considerable memoir on the Proteaceae, shew him as a naturalist imbued with keen insight and possessed of extraordinarily sound judgment.

But Brown did not confine his attention to phanerogams, but, as might have been anticipated from the studies of his earlier years, pursued his investigations into the little explored field of the cryptogams.

We have seen that as a young man he had been greatly attracted to the study of mosses. Later on he contributed two important papers on these plants to the Linnean Society, one in 1809, in which he described two new genera, one of them Dawsonia, the other Leptostomum, both from Australasia. The introductory remarks in which he discusses the character of the moss capsule, are interesting as shewing how hopelessly impossible it was at that time to arrive at a scientific understanding of its structure, so long as everything was tested by the touchstone of the flowering plants. Ten years afterwards he reverted to the same subject, describing the new genus Lyellia from Nepaul, and comparing it, as was his wont, with allied genera, e.g. Polytrichum, Buxbaumia and many others, with the view of elucidating the significance of its structure. The spores, however, are still spoken of as seeds. The male plant is generally regarded as the barren plant. It is not easy to reconcile the existence of male flowers with the view of Beauvois which Brown seemed still to consider as not disproved, viz. that the seeds and pollen were both contained in the capsule.

Mosses were not the only cryptograms to which he turned his attention. He described a new species of Azolla (A. pinnata) from Port Jackson, and the plant was illustrated by the excellent drawings of Bauer. But here, too, the time was not yet ripe for a morphological understanding of the structure. The megasporangium was thought to be the male flower, the microsporangia being interpreted as capsules containing several seeds (the glochidia). The explanation of the supposed male flower presented difficulties, but he states that the lower cell (i.e. the megaspore) was once found filled with a powder replacing the turbid fluid ordinarily occurring there, and the powder was supposed in some way to be ejected and thence to be conveyed to the female organ.

Ferns also claimed his attention, and among his other contributions he founded the genus Woodsia, calling attention to the character of the involucrum (indusium), which separated it from the other polypodia with which the species had previously been associated.

Brown had always taken a keen interest in fossil plants, although, so far as I am aware, he only wrote one paper on the subject. This one, however, was of considerable importance, for its subject was the Brownian cone of Lepidodendron, called by him Triplosporite, though its true affinities were correctly gauged.

Although, as I have said, Brown was less successful when grappling with cryptogams, he is always worth reading on any subject, and in his own special province, that of the flowering plants, I know of no one amongst the older writers from whom one may learn so much. This is due not only to the genius and erudition which he brought to bear on every problem he attacked, but also to the example he affords of scientific method in handling his subject. In his respect for accuracy, in his cautious attitude, as well as in the single-minded honesty of purpose he everywhere exhibits, he has set an example not only for his own but for all future time.

His personal character made a deep impression on his contemporaries. To his friends he was very faithful, and the unanimous tribute of affectionate (though respectful) admiration affords full proof of this. Like many other strong characters, however, he seems also to have been able at times to shew a rougher side of his nature. He was not generous with his specimens, nor was he always ready to part with information. Asa Gray tells a story of how he encountered this trait of Brown's character. Gray was visiting this country and, of course, made the great botanist's acquaintance. One day Brown told him that he knew of a character by which Rhexia (a genus in which Gray was at that time interested) could be distinguished from some nearly allied ones, and that this character had escaped the notice of De Candolle and others. But Gray could not get it out of him, and it was not till the following week that Brown was induced to part with his secret!

It is interesting to observe the impression the elder botanist made on Gray, and to note the growing admiration with which the younger man speaks of him in the very readable diary he kept of his London visit. It was the same, however, with all. The more intimate the acquaintance the more profound the respect, and sometimes the love, that Brown's personality inspired.

Brown was a keen business man, and well lived up to the traditions of the land of his birth. He gave a remarkable proof of his canniness in the successful outcome of his bargaining with the trustees of the British Museum. Sir Joseph Banks by his will had left him not only his house, but also a life user of the Banksian collections, after which they were to go to the Museum. In 1827 Brown entered into a hard agreement with the trustees to transfer the collections at once to the Museum, he being appointed "under-librarian" at an adequate salary, with a well safeguarded position. He used commonly to take 11 weeks' holiday--a length of vacation which served to differentiate him rather clearly (and to his own advantage) from his colleagues. He successfully countered all official moves designed to encroach on the terms of his agreement whereby his freedom might be curtailed, and his conditions of service be brought more into line with those that obtained elsewhere in the Museum.

He maintained through his life intimate relations with the Linnean Society. He acted during his earlier life as Librarian to the Society, an office which he resigned in 1822. Two years previously he had succeeded to the house in Soho Square which had been left to him by Sir Joseph Banks, and as it was larger than his own requirements demanded, an arrangement was made by which the Linnean Society moved into the vacant rooms, where it remained for a number of years. Brown subsequently became President of the Society (in 1849).

Robert Brown was deservedly acclaimed by his contemporaries as the first botanist of his age, and honours fell to his share even in his earlier years. He was elected a Fellow of the Royal Society in 1811, and twenty-eight years afterwards was awarded the Copley Medal. He was approached in 1819 in connection with the Chair of Botany in Edinburgh, but decided not to sever his intimate connection with Sir Joseph Banks. Abroad he was probably more widely known than in this country, for when on a visit to Prussia the King sent a special carriage to meet him, and decorated him with the Order Pour la Mérite. In England, on the other hand, though held in the highest esteem by his scientific confrères, he shared the obscurity that was the common lot of many of the savants of that age. He was, however, awarded a civil pension, although not without question on the part of certain members of the House of Commons.

He lived to a ripe age, passing away in the year 1858, the 85th of his age. To the last he retained his interest in his life work, and on June 3, a week before he died, he signed a certificate in favour of an Associate of the Linnean Society.