128 PLANT LIFE 
the structure of the organism and its environ- 
ment. It is, further, almost a truism to 
remark that the more complex the organism 
the more patent is the perfection of its 
adjustment. 
It is only when we get at closer quarters 
with our problem that its intricacies really 
begin to reveal themselves, and we are 
obliged to confess that our search for the 
causes, and even for the proximate agents by 
which the production of appropriate mechan- 
ical tissue is produced, has not been greatly 
rewarded. Of the means whereby the corre- 
lation is secured between functional need on 
the one hand, and its peculiarily correct 
satisfaction on the other, we have no positive 
knowledge at all. 
It is easy to talk of “‘ capacity to vary,” 
** survival of the fittest,’ and so on. Such 
formule have their uses as expressing rather 
clearly certain definite facts, and as indicat- 
ing in a general way some of the probable 
or possible processes which have been con- 
cerned in, or have at least influenced, the 
modification of plants and animals in their 
long course of evolution. But, after all, they 
are only generalised descriptions, and give 
us very little real or direct insight into the 
nature of the processes themselves, and yet 
it is precisely in the latter that the whole 
secrets of evolution, and all that it implies, 
are contained. In the particular example 
we have been considering, we want to know 
