FUNCTION AND FORM 89 
position as regards the source of light, would 
be as useless as a heavily shaded one. More- 
over, with the increase of the leaves the 
mechanical requirements vitally affect the 
whole subsidiary apparatus of the plant. The 
root is concerned in this no less than the stem, 
for the leaf depends for the proper discharge 
of its functions on an adequate degree of 
fixity on the part of the plant as a whole. 
Another factor which materially influences 
the foliar organs of a plant, lies in the 
water supply, for if this be deficient or 
precarious, the leaf area must. either be 
correspondingly reduced, or there must be 
found some means of checking the loss of 
water, or else the difficulty must be met in 
yet other ways. The particular form of solu- 
tion of the water problem which happens to 
be adopted by any given plant is a matter 
that will mainly depend, as already pointed 
out, on its own inherent constitution. 
It is worth while to endeavour to follow out 
some of the numerous and diverse ways by 
which those problems relating especially to 
mechanical needs and to water supply have 
been solved by various sorts of plants. Not 
only shall we encounter remarkable examples 
of adaptedness to special conditions, ‘but we 
shall incidentally be brought into close con- 
tact with some of the more difficult questions 
of biological philosophy. 
In any event we shall gain a clearer idea 
of the way in which the whole anatomical 
