LEAF-STRUCTURE AS RELATED TO ENVIRONMENT 
latter. When the wind velocity was high or if it came in gusts there 
was less difference in the air movement within the crown and at the 
south periphery than when the velocity was low. This is explained by 
the fact that the leaves and branches were more effective in keeping the 
wind out of the crown when the wind velocity was low than when it 
was high. As the wind velocity was not the same when all the read- 
ings were made, the ratios of the various trees cannot be directly com- 
pared with each other. It is highly probable that if readings were 
taken on Acer negundo under the same velocity as on Acer saccharum, 
i. e., 68.9 meters per minute instead of 58.6, the ratio of wind in the 
crown to that of the south periphery would be less than i : 1.3. In the 
case of Acer saccharum as high a ratio of crown to south periphery as 
i: 8.1 was found when the wind velocity was regular and fairly 
low. 
Readings were taken with two cup anemometers on a Fraxinus 
pennsylvanica near Lincoln. The readings were made every half 
hour from 9:45 A.M. to 3:45 P.M. As the wind came from the north- 
west, readings were made at the northwest periphery and within the 
crown. The wind velocity within the crown was found to vary from 
32 percent to 52 percent of that at the northwest periphery. At 9:45 
A.M. the velocity within the crown was 3.7 kilometers per hour and 
at the northwest periphery 11.6. At 3:45 P.M. the velocity within 
the crown was 6.6 km., and at the periphery 12.7 km. 
Effects of the Physical Factors 
I. Transpiration 
Method 
Branches from the center of the crown and from the south periph- 
ery, bearing numerous leaves were cut under water. These 
branches were securely fastened by rubber tubing to the base of bu- 
rette tubes graduated to tenths of cubic centimeters. The amount of 
water in each tube was about equal throughout the experiment, so 
that there would be no error due to unequal heads of pressure. The 
tubes, with the branches attached so as to be upright, were fastened in 
representative situations in the center or at the south periphery. 
Readings were usually taken simultaneously in both situations every 
15 minutes. The leaf area was measured from prints on Kresko paper 
by means of the planimeter. 
