20, 2 Trelease: Foliar Transpiring Power of Coconut 171 
a relative value in terms of the percentage of the range from 
the lowest to the highest actual value. These relative values, 
reduced to this uniform basis are presented graphically in fig. 1, 
in which the dot and dash line represents transpiring power; 
the full line, apparent pinna width; and the dash line, evaporat- 
ing power of the air. 
Inspection of the graph of foliar transpiring power (dot and 
dash line) shows that this has its maximum value at 6 a. m.,; 
a short time after sunrise. Approximately the maximum was 
maintained until 11 a.m. Then the index of transpiring power 
decreased rather gradually and uniformly until 8 p. m., and then 
decreased rapidly to a low night value. This low night index 
was maintained approximately constant until 2 a. m. From 
2to4a.m. there was a slight increase in the index of transpiring 
power, and from 4 to 6 a. m. there was a rapid increase to approx- 
imately the maximum value. The graph of the daily march of 
transpiring power of coconut thus resembles in a general way 
the published graphs showing transpiring power for other kinds 
of plants studied by the same method.’ It is worthy of men- 
tion, however, that the maximum occurred earlier in the day 
for coconut than for other plants tested, and that the decrease 
in transpiring power therefore occurred earlier. Also, in coco- 
nut, although there was a fall in transpiring power during the 
time of approximately maximum evaporation rates, there was 
not the subsequent pronounced rise found by Bakke(3) for 
Helianthus. 
Inspection of the graph (full line) that represents changes 
in the distance between the edges of the pinnae shows that 
this apparent width decreased uniformly from 6 a. m. until noon, 
and then increased uniformly until a maximum width was reached 
at 10 p. m.; this maximum was then maintained throughout the 
remaining hours of darkness. This graph illustrates the kind 
of change that is usually observed during the day in the apparent 
‘Width of the pinnae. It is interesting to compare this graph 
with the graph (dash line) representing the hourly changes in 
the evaporating power of the air. Such a comparison shows 
that the changes in the evaporating power of the air exhibited a 
general inverse relationship to variations in the apparent width 
of the pinnae, since the evaporating power increased from 
6 a. m. until noon and then decreased in the afternoon and reached 
a very low value after dark, the low value being maintained 
*See Bakke, (1, 2, 3, 4) Livingston,(6) Shive and Martin,(12) and Tre- 
lease and Livingston. (14) 
