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K.—BOTANY. 253 
do not know that it is necessary to explain them thus: they may be 
brought about in other ways. Epharmosis in the widest sense means 
simply the continuous adjustment of the organism to its conditions of 
life. It is often used with reference to external conditions only, but 
we should not forget that adjustment to external conditions cannot be 
separated, except by logical abstraction, from the total adjustment of 
the organism, internal and external. The ontogenesis of each indi- 
vidual is a continuous process of adjustment of every part of the organ- 
ism to its internal and external environment. So much follows from 
the universal law that every physical system constantly tends towards 
equilibrium, and the law is abundantly illustrated in the development 
of plants. The particular state of relative equilibrium represented by 
the adult individual is, however, as we know, mainly determined by 
the stock of genes contained in the zygote from which it is developed, 
though partly by the particular environment in which it grows up. 
Epharmosis as a theory of phylogenesis must depend on the belief 
that the genes themselves can be considerably, continuously, and per- 
manently altered by forces outside themselyes—their environment in 
the wide sense—and it must be admitted that the evidence for such a 
belief is neither very abundant nor very conclusive. We certainly do 
not know that genes cannot be so altered; but we cannot point to cases 
in which it is possible either to assert definitely that they are or to 
explain plausibly how they may be. On this side the Neo-Darwinian 
position has not yet, as it seems to me, been successfully attacked, 
though few biologists who are interested in these questions and not 
wedded to a particular theory of evolution would now be greatly sur- 
prised if it eventually fell. 
How, then, are we to make progress to a fuller knowledge of the 
necessarily interlinked problems of phylogenesis and ontogenesis which 
together make up the problem of evolution? On the one hand we 
have the theoretically indispensable genes, of whose nature we have 
no certain knowledge, though we know a great deal now about the effect 
on the phenotype of various combinations and omissions of some among 
them. On the other we have the phenotype, built up from the genes 
by long and complicated processes of physical and chemical action and 
interaction between the genes and their derivatives, between the sub- 
stances and structures of the developing organism, and between these 
and the environment. Of these ontogenetic processes we still know 
extraordinarily little. Until quite recently physiology has kept its face 
averted from such problems, partly as a result of that unfortunate 
divorce from morphology which we have seen emphasised as a cardinal 
principle of botanical methodology by distinguished botanists. It must 
be admitted that these processes are difficult to disentangle, and it is 
only the great development of physical chemistry, and of the so-called 
biochemistry which depends so closely upon it, that has opened up 
during the last twenty years the avenues through which we may 
approach the problems in this field with any prospect of success. Thirty 
years ago plant physiologists were mostly either occupying themselves 
with measuring the ‘ functions ’ of the organs of the adult plant under 
different conditions, or they were caught in the toils of the ‘ stimulus 
