554 
HERBERT C. HANSON 
The amount of evaporation at the base was 57 percent that of the 
apex, and the Hght intensity at the base was o.oio. 
Acer saccharinum. — Isolated individuals of Acer saccharinum were 
studied in Minneapolis and Lincoln. The center leaves of the tree in 
the former place were 66 percent the thickness of the south periphery 
Figs. 16-17. Fraxinus pennsylvanica. Fig. 16, Isolated tree. Leaves from 
south periphery. Fig. 17, Isolated tree. Leaves from center of crown. Fig. 18. 
Quercus rulra. Forest tree. Leaves from base. 
leaves. Most of this increase was caused by the palisade as the thick- 
ness of the palisade in the former was but 48 percent that of the latter. 
In the center leaves the palisade made up 39 percent; the sponge, 32 
percent; the upper epidermis, 16 percent; the lower epidermis. 13 per- 
cent of the total thickness. In the south periphery leaves the palisade 
made up 53 percent; the sponge, 26 percent; the upper epidermis, 
II percent; the lower epidermis, 9 percent of the total thickness. 
The center leaves had one layer of loose palisade while the south 
periphery leaves had one or two layers composed of larger and more 
compactly arranged cells. The entire structure of the south periph- 
ery leaves was more compact and there was greater development of 
