324 BOTANICAL GAZETTE [APRIL 
(2.94 cc. per hour, table II). In the third test the water variation 
was slightly (probably within the limits of experimental error) in 
the opposite direction, as has been noted. The evaporation maxi- 
mum on this day was relatively low, 2.52 cc. per hour (table IV). 
These relations make it appear that the amount of variation in 
foliar moisture is directly related to the evaporating power of the 
air, especially to the maximum intensity of this factor for the day 
TABLE IV 
AUGUST 30, 1910 
EVAPORATION PERCENTAGE OF MOISTURE 
Physalis angulata 
Period cc. per hour Hour of test 
On basis of On basis of 
dry substance entire weight 
(A.M.) 
Yee =. 07 7 668.2 87 
8-9 ¥.50 9 695.0 4 
Q-I0 mre & ocr eae IT SEE ey Ini aera, CPE een ar 
IO-II 2.46 II 680.7 87 
II-I2 DNs C2 SER STEN [es ge Mae any Wee Rees ene aay 
(P.M.) 
I2- 1 2.30 I 714.7 88 
I- 2 rere 
2- 3 2.36 3 662.3 87* 
oon « ete ne ay ie yaork 
4:30-5:30 0.97 5:30 665.7 87 
—The day was — wholly cloudy, which accounts for the generally low evaporation 
rates pry she small fluctuation 
in question. With great evaporation there appears to be a great 
diurnal fall in moisture content, with less evaporation a less pro- 
nounced fall, and with still less evaporation no fall at all, possibly 
even a slight rise. 
Only a single test, with measurement of evaporation, was carried 
out with each of the remaining forms. The greatest variations 
were exhibited by Martynia, Amarantus, and Sida, all of them 
being plants which have been repeatedly observed to wilt very 
readily under drought conditions. The only true succulent tested 
was Trianthema, which showed a variation markedly greater than 
that of Physalis for the same day (table II). Nicotiana and 
