256 SECTIONAL ADDRESSES. 
imagination of biologists, the first brilliant results of the evolutionary 
interpretation of the doctrine of homology, led to an interest in structure 
for its own sake which could have but a limited fertility. This interest 
has in the loag run been mainly important because it has immensely 
increased our actual knowledge of structure. At the same time the very 
human but really quite irrational desire to find a ‘ use’ for everything 
led to a facile and sweeping application of the theory of natural selection 
quite out of accord with the patent facts of nature. The physiologists, 
the people who really remained interested in tracing causal sequences, 1n 
finding out ‘ how things work,’ and who retained the only sound method 
of discovering this—the experimental method—were rather cut off from 
the interpretation of structure by the assumption that it was causally 
‘explained’ if it were shown or even plausibly believed to be useful to 
the organism, and tended to confine themselves to measuring and deter- 
mining the conditions of processes, mainly in the adult plant. Thus 
there came about that separation of morphology from physiology which 
was no doubt a sound methodological principle for the restricted purpose 
of increasing our knowledge of certain series of facts, but which in its 
general effect on botany has, I fear, tended not only to disruption but 
to sterilisation. The effect of the divorce between morphology and 
physiology was just as bad for physiology as it was for morphology. 
As little accustomed as the morphologist himself to envisaging the plant 
in its entirety as a continuously developing complex of substances and 
structures, the average physiologist tended to limit himself, as has 
been said, to the recording and measuring under different conditions of 
arbitrarily selected functions or processes, with the result that his work 
was often at least as arid as the conventional descriptions and correla- 
tions of the morphologist. Needless to say, there were honourable 
exceptions in both camps. 
It is instructive in this connexion to consider a work which pro- 
fessed to deal with tissue structure in the light of function or process— 
a book thoroughly characteristic of the period I have been considering, 
the first edition being published in 1884 and the latest (the fifth) in 1918 
—I mean Haberlandt’s ‘ Physiologische Pflanzenanatomie.’ This book 
describes and discusses each of the tissue systems of the higher plant 
from the point of view of the part which it plays in carrying on the 
life functions of the plant as a whole, an excellent aim, and one which 
is, in the main, admirably carried out. The author makes a great 
point of adducing experimental evidence for the ‘ functions’ of par- 
ticular tissues wherever possible. But there is always the implicit 
assumption that every tissue must have a ‘ function,’ must be of some 
“use ’ to the plant, and in his effort to find that use Haberlandt is 
often compelled to rely on unconvincing argument from structure or 
from analogy, sometimes on little more than guesswork. It scarcely 
seems to occur to him that a tissue may have no specific ‘ use’ at all, 
that structures are developed as the result of the processes which take 
place in the developing plant, and do not necessarily perform a definite 
function which is useful to the whole organism. Many of them do, 
of course; but to confine oneself to the search for such ‘ functions ’ is 
ee 
