LEAF-STRUCTURE AS RELATED TO ENVIRONMENT 553 
the lower epidermis, ii percent of the total thickness. In the apex 
leaves, the palisade made up 57 percent; the sponge, 25 percent; the 
upper epidermis, 12 percent; the lower epidermis, 6 percent of the 
total thickness. 
Figs. 12-13. Quercus macrocarpa. Fig. 12, Isolated tree. First growth leaves 
from south periphery. Fig. 13, Figure represents first and second growth leaves 
from isolated tree, center of crown ; and forest tree, base of crown. 
Figs. 14-15. Acer saccharinum. Fig. 14, Isolated tree. Leaves from center 
of crown (Lincoln). Fig. 15, Isolated tree. Leaves from south periphery. 
As in the leaves already studied the chief differences in structure 
consisted in the increase in palisade tissue and the greater compactness 
of the tissue in the apex leaves. From two to four layers of palisade 
were found in the apex leaves, while only one was found in the base 
leaves. The cells in the former leaves were more prolate in shape 
than those in the latter. The apex leaves had greater bundle de- 
velopment than the base leaves. The weight of the base green leaves 
was 58 percent, the weight of the water-free leaves 47 percent the 
weights of the corresponding apex leaves. The water content of the 
former leaves was 63 percent, of the latter 54 percent. 
