By FRANCIS DARWIN, Honorary Fellow of Christ's College, Cambridge.
My father's interest in plants was of two kinds, which may be roughly distinguished as EVOLUTIONARY and PHYSIOLOGICAL. Thus in his purely evolutionary work, for instance in "The Origin of Species" and in his book on "Variation under Domestication", plants as well as animals served as material for his generalisations. He was largely dependent on the work of others for the facts used in the evolutionary work, and despised himself for belonging to the "blessed gang" of compilers. And he correspondingly rejoiced in the employment of his wonderful power of observation in the physiological problems which occupied so much of his later life. But inasmuch as he felt evolution to be his life's work, he regarded himself as something of an idler in observing climbing plants, insectivorous plants, orchids, etc. In this physiological work he was to a large extent urged on by his passionate desire to understand the machinery of all living things.
But though it is true that he worked at physiological problems in the naturalist's spirit of curiosity, yet there was always present to him the bearing of his facts on the problem of evolution. His interests, physiological and evolutionary, were indeed so interwoven that they cannot be sharply separated. Thus his original interest in the fertilisation of flowers was evolutionary. "I was led" ("Life and Letters", I. page 90.), he says, "to attend to the cross-fertilisation of flowers by the aid of insects, from having come to the conclusion in my speculations on the origin of species, that crossing played an important part in keeping specific forms constant." In the same way the value of his experimental work on heterostyled plants crystalised out in his mind into the conclusion that the product of illegitimate unions are equivalent to hybrids--a conclusion of the greatest interest from an evolutionary point of view.
And again his work "Cross and Self Fertilisation" may be condensed to a point of view of great importance in reference to the meaning and origin of sexual reproduction. (See Professor Goebel's article in the present volume.)The whole of his physiological work may be looked at as an illustration of the potency of his theory as an "instrument for the extension of the realm of natural knowledge." (Huxley in Darwin's "Life and Letters." II. page 204.)His doctrine of natural selection gave, as is well known, an impulse to the investigation of the use of organs--and thus created the great school of what is known in Germany as Biology--a department of science for which no English word exists except the rather vague term Natural History. This was especially the case in floral biology, and it is interesting to see with what hesitation he at first expressed the value of his book on Orchids ("Life and Letters", III. page 254.), "It will perhaps serve to illustrate how Natural History may be worked under the belief of the modification of species" (1861). And in 1862 he speaks (Loc. cit.) more definitely of the relation of his work to natural selection: "I can show the meaning of some of the apparently meaningless ridges (and) horns; who will now venture to say that this or that structure is useless?" It is the fashion now to minimise the value of this class of work, and we even find it said by a modern writer that to inquire into the ends subserved by organs is not a scientific problem. Those who take this view surely forget that the structure of all living things is, as a whole, adaptive, and that a knowledge of how the present forms come to be what they are includes a knowledge of why they survived. They forget that the SUMMATION of variations on which divergence depends is under the rule of the environment considered as a selective force. They forget that the scientific study of the interdependence of organisms is only possible through a knowledge of the machinery of the units. And that, therefore, the investigation of such widely interesting subjects as extinction and distribution must include a knowledge of function. It is only those who follow this line of work who get to see the importance of minute points of structure and understand as my father did even in 1842, as shown in his sketch of the "Origin" (Now being prepared for publication.), that every grain of sand counts for something in the balance. Much that is confidently stated about the uselessness of different organs would never have been written if the naturalist spirit were commoner nowadays. This spirit is strikingly shown in my father's work on the movements of plants. The circumstance that botanists had not, as a class, realised the interest of the subject accounts for the fact that he was able to gather such a rich harvest of results from such a familiar object as a twining plant. The subject had been investigated by H. von Mohl, Palm, and Dutrochet, but they failed not only to master the problem but (which here concerns us) to give the absorbing interest of Darwin's book to what they discovered.
