FUNCTION AND FORM 87 
plant, while the other will readily tolerate 
shade. 
This toleration only applies to the plant 
taken as a whole, and there are limits beyond 
which endurance of shade does not go. Most 
people who have wandered through a dense 
and well-tended wood must have been struck 
by the great difference between the forms of 
the individual trees which compose it and 
those of the same species grown in the open 
or in the hedgerow. The clean tall trunks 
and the compact small crown of the forest 
tree contrast strongly with the spreading 
growth of the park specimen. And yet the 
difference is merely a consequence of the 
different conditions of illumination. A tree 
grown in the open exposes its leaves to light 
on all sides. The spreading limbs space out 
the foliage and the leaves are all more or less 
actively functional. But closer inspection 
reveals the fact that it is only the leaves on 
the periphery of the tree and its branch 
systems which are thus flourishing. The 
inner portion is bare of leaves, or at any rate 
comparatively so. This is because the inner 
twigs which become shaded by the outer 
ones are starved, and sooner or later they die 
and fall off. The leaves they bore did not 
act efficiently, and they were quietly crushed 
out of existence. 
Precisely the same thing, on a different 
scale, happens when young trees are grown 
close together, as in a well-managed forest. 
