Origifi and Development of the Composite?. 71 
Coulter (13) defines orthogenesis as “progressive evolution in 
a given direction, in contrast with the more or less successful 
variations in several directions involved in the theories of natural 
selection and mutation.” He considers orthogenesis to be a response 
to evolution of climate (cp. X, 43, Chap. XXX), i.e. to “ a persis¬ 
tent change in the conditions of living.” This, as he points out, 
makes orthogenesis a physical rather than a vitalistic phenomenon 
and such a view explains most, if not all, orthogenetic 
development. 
Throughout the Compositae Coulter’s explanation is satisfactory. 
Such cases as the tendency to dorsiventrality in the Tristichaceae 
and Podostemaceae, however, seem to require correlation in 
addition to epharmosis for their complete explanation. It is note¬ 
worthy also, that most lines of orthogenesis can be explained by 
loss of factors. All the cases of reduction or aggregation of parts, 
which form the chief examples of orthogenesis, are clearly retro¬ 
gressive mutations, e.g. the keynote of the evolution of green plants 
is generally recognised to be the progressive sterilisation of 
potentially reproductive cells. 
Epharmosis 
In its original sense, as used by Vesque (53) epharmosis is 
distinguished from adaptation ; adaptation is described as the effect 
of epharmosis after the effect has been transmitted by heredity and 
fixed by selection (op. cit., p. 44), but it is proposed to use the term 
epharmosis here as meaning the act of developing epharmony in 
Cockayne’s sense of the word (see above, Action of Environment* 
Chap. X, A). This limits epharmony to adaptations which are the 
direct result of an environmental stimulus and excludes such 
changes as may be due to mutations or other spontaneous varia¬ 
tions, and which may happen to be advantageous, while at the same 
time it removes the distinction between fixed and unfixed variations. 
There is as yet no direct evidence either for or against the fixation 
of epharmonic characters, but there are a large number of facts t 
which can be used to prove the probability of such fixation in 
plants. 
The powerful effect of environment in producing advantageous 
modifications of structure or physiological behaviour is implicit in 
much of the theorising on the origin of land plants. It is very 
significant also that Sargant, Hill, and Henslow, with three different 
theories, all attribute the origin of monocotyledony to an action of 
environment, which in all three cases is more or less direct (see 
