118 PLANT LIFE 
the same, but the real causes responsible for 
its appearance are equally obscure. ‘The most 
we can at present say is that in the exercise 
of the function new conditions are introduced 
which lead to the supply of abundant nutritive 
material, together with the power to use it. 
But the mode of interaction of all the inner 
functional conditions is far too complex for 
us to express the matter in any rough-and- 
ready formula. Least of all is it useful to say, 
in anthropomorphic fashion, that structural 
peculiarities like those of climbers are due to 
the plant having adapted itself to its environ- 
ment. We readily discern that the plant is 
adapted, but we know remarkably little about 
the processes whereby this interrelation has 
been brought about. It conduces neither to 
clearness of judgment nor to the advance 
of science to mistake more or less fanciful 
descriptions for real explanations of complex 
phenomena. 
Groups of plants such as climbers are 
interesting for the very reason that they serve 
to illustrate the fact that any species, what- 
ever its ancestral origin, may join a specialised 
biological class provided it has the capacity 
for developing an appropriate structure. 
Another biological group is constituted by 
the higher water plants. These have, for the 
most part, descended from terrestrial fore- 
bears, and they display many significant 
features of interest in connection with their 
more recent environmental conditions. Some 
