550 
HERBERT C. HANSON 
water storage cells are more poorly developed, the crystals are less 
numerous, and the side walls of the epidermal cells are more wavy. 
The weight of the green leaves from the center was 58 percent the 
weight of the south periphery leaves, the weight of the water free 
leaves from the center 51 percent. The water content of the center 
leaves was 65 percent, of the south periphery leaves 60 percent. 
The amount of evaporation and the wind in the center were 77 
percent and 65 percent of the amounts at the south periphery. The 
light intensity in the center was 0.0353. 
The center leaves of an isolated tree examined in Lincoln had 
thicker leaves than the isolated tree in Minneapolis, although the 
south periphery leaves were thinner. As the light intensity in the 
center was 0.115, and the evaporation 59 percent that of the south 
periphery; it seems probable that the increase in light intensity ac- 
counts for the increase in the leaf thickness. 
As in Acer saccharum the leaves on forest individuals of this species 
are thinner than on isolated individuals. The apex leaves of forest 
trees are about the same thickness as the south periphery leaves of 
isolated trees, while the base leaves of the forest trees are 69 percent 
the thickness of the center leaves of isolated trees. The decrease in 
thickness may be accounted for by the increased humidity and the 
lower light intensity, o. 00865, in the forest; as compared with the 
isolated tree. 
The second crop leaves from the base of the forest individuals were 
thicker (31 percent) than the first crop while the apex leaves were 
thinner (17 percent). The weight of the green leaves and the weight of 
the air-dried leaves at the base were 29 percent and 20 percent that 
of the apex leaves per given area. Although the difference in the 
thickness of the first and second crop apex leaves was only 17 percent, 
the structure of the second crop leaves was far more mesophytic as 
seen in the amount of air space, number of bundles, and water storage 
cells. 
Qtiercus macrocarpa. — ^The center leaves of a well-formed, typical 
isolated tree were 61 percent of the thickness of the south periphery 
leaves. The increase in thickness was due chiefly to the increased 
development of palisade tissue. The amount of pahsade in the center 
leaves was 37 percent of that in the south periphery leaves. The 
amount of sponge in the center leaves was over twice as great as in the 
south periphery leaves, showing that most of the sponge tissue had 
