THE FOREST CANOPY 35 
are, of course, many interruptions in the canopy. 
As forestry is applied a more uniform canopy grad- 
ually develops. For example, a wide-spreading pri- 
meval tree, having reached maturity in the natural 
woods, is removed. In its place hundreds of seed- 
lings appear. These form a group or hurst, with a 
canopy. Several groups may often be united, or the 
same group extended to meet other groups by plant- 
ing, so that in time a uniform canopy may be devel- 
oped over a considerable area. 
Owing to the fact, however, that some species 
need less ight than others, there is a strong tendency 
toward irregularity of canopy in mixed woods. Trees, 
in this respect, may be divided into three classes— 
light demanders, shade endurers, and shade demand- 
ers. The fact that some trees are shade demanders 
in youth and light demanders later adds to the diffi- 
culty in caring for woods in proportion to the nature 
and extent of the mixture. This relation of species 
to light causes a differentiation in the nature of the 
canopy. The canopy may become, therefore, com- 
pound or storied. On the top is that story of the 
canopy which belongs to the light demanders; next, 
the story which belongs to the shade endurers, and 
also, in the tropics, where light is abundant, a story 
of shade demanders. Nothing is more important to 
the silviculturist than a knowledge of the light re- 
