262 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
of coconut is usually higher in the night than during the day is apparently 
related to higher water content of the plant as a whole in the night — at 
least to greater turgidity in the enlarging parts. 
A comparison of the hours of occurrence of the minimum expansion for 
the three sets of pinnae measured (three different plants) shows that there 
was no constant relationship between the three sets as to the time of greatest 
drooping of the wings, though the minimum for plant C usually occurred 
earlier in the day than did the minima for the other two plants. From this 
variation it again appears (as was suggested by the tests with excised pieces) 
that individual differences between plants or leaves may result in somewhat 
different responses in incipient drying and wilting. The temperature and 
evaporation data given in table 2 show that in these tests the maximum 
temperature occurred between i p.m. and 4, usually between i p.m. and 3; 
and that the maximum evaporation rates occurred between noon and 3 p.m., 
most frequently about 2 p.m. or 3. Minimum temperature is shown in 
all cases for 6 a.m., and the minimum evaporation rate is shown for each 
day (except during rainfall on May 2) as occurring between 7 a.m. and 8. 
Had night readings been taken, they would undoubtedly have shown lower 
rates of evaporation than any during the day. A comparison of the 
recorded fluctuations in temperature and evaporation with corresponding 
fluctuations in wing position shows that the minimum leaf width usually 
occurred within one or two hours of the occurrence of the maximum tempera- 
ture and the maximum evaporating power of the air, but that there was 
no very constant relation between these variations. If pinna expansion 
depends upon the turgidity and water content of the hinge cells, it would 
not be expected that a simple relationship would exist between either 
temperature or evaporation and angular divergence, since these external 
conditions affect the water content of only indirectly effective cells, by 
influencing the rate of water loss from the leaves and that of water absorp- 
tion by the roots. 
The. hourly variations in the wing position for these coconut leaves re- 
semble similar variations that other workers have observed in water con- 
tent and wilting for many other kinds of plants. Thus the minimum 
water content observed by Livingston and Brown (7) occurred usually 
within an hour or two of the time of highest evaporation rates, the minimum 
moisture content of the leaves of most of their plants occurring between 
I p.m. and 5. Lloyd (9) found that the water content of the leaves of 
Fotiquieria splendens began to decrease at daybreak and reached a minimum 
some time between noon and 4 p.m.; after that time the water content 
increased until about 4 a.m. With the cotton plant Lloyd (10) found that 
the minimum water content of leaves was reached at about 2 p.m. Miller 
(11), studying maize, milo, and kafir, found that all three of the plants 
showed a decreased water content between 7 a.m. and 11; in one third of 
his observations on maize and milo and in one fifth of those on kafir, the 
