LEAF-STRUCTURE AS RELATED TO ENVIRONMENT 
547 
the light intensity and the evaporating power of the air were greater 
than when the first crop developed. In the former case less solid 
material, and in the latter, more solid material would form in the leaf 
cells. 
4. Comparison of Leaf Structure 
The detailed microscopical study and measurements of the leaf 
structure of various trees are summarized in the following observations 
for each species. This detailed study was made upon cross sections 
of from five to ten representative leaves from each position of the trees. 
All figures are made from photographs of camera lucida drawings of sections of 
leaves. The leaves were taken from the various positions indicated below. Except 
as indicated, all material Vv^as from the vicinity of Minneapolis, Minn. 
Figs. 1-4. Acer saccharum. Fig. i, Isolated tree. Leaves from south periphery. 
Fig. 2, Isolated tree. Leaves from center of crown. Fig. 3, Forest tree. Leaves 
from base. Fig. 4, Forest, seven-year-old tree. Leaves from base. 
The trees were selected carefully so as to secure specimens typical of 
the species. Permanent mounts of these sections were made by the 
parafhn process. Care was taken so that the sections were cut from 
