Perhaps I shall not be accused of going too far if, finally, I consider a moment the somewhat phantasmically spun threads which bind plant physiology with psychology. I have in mind that work of Fechner, the founder of psychophysics, published in the stormy year of 1848, a book written with the tenderest human sympathy. It had been formerly thought that plants were incapable of locomotion, and on that basis were distinguished from animals. This view was refuted by the same facts which destroyed the long-held opinion as to the insensibility of plants. Now, the last year has brought valuable explanations of the power of sensation in plants, and many fancies of Fechner's as to the sensibility of plants have been transformed into scientifically grounded views. The reception and conduction of stimuli and response to them, as in the nervous system of animals, have been demonstrated, although these organisms have no nerves, but, as Fechner said, function often as if they had nerves. If, now, plants possess a soul in the sense employed by modern psychology, then intimacy with the life of plants would offer the psychologists much support in testing the psychical functions from the standpoint of the unity of all organized beings, and the more exact separation of these psychic functions from other life functions.
I hasten to the close, and must leave unconsidered many important relations of plant physiology to the other sciences. I have not mentioned the studies upon the adaptation of flowers to insects, and vice versa, resulting in fruit production in the former—studies which call into existence a new borderland between zoology and plant physiology. I omitted also to mention the physiological elements in plant geography, also the great assistance which mathematics has rendered our science, and must likewise pass over much besides.
I have been able to trace only in a few characteristic examples the results which issue from a consideration of the relation of plant physiology to the other sciences. Essentially my whole treatment of the subject has been merely an example, for whatever holds true in my specialty holds true likewise in every other branch of knowledge, namely, the very intimate union of each with other, often widely separated, branches of learning—a union which, with the progress of research, assumes constantly greater power.
The relation of the individual branches of science to each other proves to be so complicated, as is clear from the examples cited, that we may well conceive how all attempts must be frustrated which, from Bacon to d'Alembert and from the encyclopedists to the present time, had for their object a classification of the sciences. One can not parcel off the sciences like a building plot. We ourselves have drawn the division lines between the individual sciences, compelled by the limitations of our human mind, which necessitates us to make a division of labor. But with our advances these boundaries disappear; the individual studies, often inimically opposed, unite into a single whole. Thus science
