LEAF-STRUCTURE AS RELATED TO ENVIRONMENT 
become palisade. In the center leaves the palisade made up 46 per- 
cent of the total thickness; the sponge, 34 percent; the upper epidermis 
13 percent; the lower epidermis 7 percent. In the south periphery 
leaves che palisade made up 75.8 percent of the total thickness; the 
Fig- 9- Quercus macrocarpa. Isolated tree. Second growth leaves from south 
periphery. 
Figs. lo-ii. Acer saccharinum. Fig. 10, Isolated tree. Leaves from south 
periphery (Lincoln). Fig. 11, Isolated tree. Leaves from center of crown. 
Sponge 7.8 percent; the upper epidermis 10.6 percent; the lower epi- 
dermis 5.8 percent. The weight of the green leaves and the weight 
of the water-free leaves in the center were 66 percent and 46 percent of 
those at the south periphery. The water content of the former leaves 
was 61 percent, of the latter leaves 43 percent. 
The amojnt of evaporation and the rate of the wind in the center 
were 75 percent and 50 percent of the amounts at the south periphery. 
The light intensity at the center was 0.148. Another isolated tree, 
having a more open crown, showed an increase in the south periphery 
leaves of about 3 percent and in the center leaves of about 12 percent. 
