552 
HERBERT C. HANSON 
Both the south periphery (22 percent) and center (13 percent) second 
crop leaves of this tree were thicker than the first crop leaves. The 
increase in the compactness of the palisade tissue in the south periph- 
ery leaves was especially noticeable. 
The base leaves of forest individuals were thinner than the center 
leaves of isolated trees. The light intensity in which these leaves 
grew was 0.075 and the amount of evaporation 46 percent of that at 
the apex. The apex leaves were slightly thicker than the south 
periphery leaves of isolated trees. The thickness of the base leaves 
was 47 percent that of the apex leaves and the thickness of the palisade 
in the former was 30 percent that of the latter. 
Quercus rubra. — An individual of Quercus rubra growing in an 
Acer saccharum and Tilia americana forest was studied. The lowest 
leaves, 7.3 m. high, were 67 percent the thickness of the apex leaves, 
12.8 m. high. The difference in the amount of palisade in the leaves 
from the two positions was not so great as in the trees so far noted. 
The thickness of the palisade in the base leaves was 57 percent that of 
the apex leaves. In the base leaves the palisade made up 44 percent; 
the sponge, 30 percent; the upper epidermis, 16 percent; the lower 
epidermis, 10 percent of the total thickness. In the apex leaves the 
palisade made up 52 percent; the sponge, 26 percent; the upper epi- 
dermis, 15 percent; the lower epidermis 7 percent. 
The chief differences in structure were that the apex leaves often 
had three layers of palisade cells, while the base leaves had two; the 
palisade was more compact and composed of longer cells, and there 
was a decrease in the air-space and an increase in the water storage 
cells and fibro-vascular bundles in the apex leaves. 
The weight of the green leaves at the base was 63 percent that of 
the apex leaves, the weight of the water-free leaves 58 percent. The 
water content of the former was 52 percent, of the latter 49 percent. 
The amount of evaporation at the base was 58 percent that of the 
apex, and the light intensity at the base was 0.0425. 
Quercus alba. — The Quercus alba studied grew in the forest very 
near the Quercus rubra. The base leaves, 35 m. high, were 64 percent 
the thickness of the apex leaves 9.2 m. high. The thickness of the 
palisade in the base leaves was 38 percent that of the apex leaves. 
The thickness of the sponge and the lower epidermis was less in the 
latter than in the former. In the base leaves the palisade made up 
33 percent; the sponge, 41 percent; the upper epidermis, 15 percent; 
