1918] BAKKE—WILTING 85 
are at night. The average day values are accordingly 0.72, 0.92, 
0.74, 0.38, 0.26, 0.19, 0.32 for one set (Ia); for the other (Ib), 
0.61, 0.89, 0.76, 0.30, 0.30, 0.39, 0.42. The average night 
values for the first series are 0.29, 0.34, 0.24, 0.19, 0.25, 0.44, 
0.69; for the second series, 0.31, 0.39, 0.23,0.16,0.50,0.45,0.61. 
The results obtained by calculating the ratio of the respective day 
and night values are rather uniform. For August 16 the average 
ratio is 2.4; for August 17, 2.7; the remaining values for Ia are 
3-1, 2.0, 1.0, 0.43, 0.46. The corresponding respective values 
jor series ID are 2.0, 2.3,°'3.3, “£9, 0.97, 0:87, 0.61. For 
the first two days, August 16 and 17, the probable normal ratio 
is between 2 and 3. On the following day there is a slight increase, 
and after that there is a decrease. Whether the rise in the ratio on 
the third day presents a normal situation or not cannot at present 
be stated; at any rate the value is not far from 3. The decrease 
in foliar transpiring power after August 19 and the resulting 
decrease in the ratio do not show any definite mathematical relation. 
For a plant growing in a normal environment, a rise in evaporation 
will give an increase in transpiring power, but on August 22 there 
is a high evaporation, a low foliar transpiring power, and a lower 
day value than night value. Such a status must be looked upon as 
abnormal for growing plants. Beginning with August 21 there is a 
rapid ascent. 
Considerable agreement is present between the graphs in this 
series and the one for Helianthus (3), where the plants were 
lifted from the soil. There is a decrease in the foliar transpiring 
power to a point where there is more or less of a balance, and then 
again where there is an increase. The time element in the present 
series is extended over a longer period, and as a result variations 
which might be masked in the series of short duration would be 
present. 
The rupture of the water columns of the plants of the 1915 
series is as definite as that presented for the plants lifted from the 
soil in southern Arizona. The outstanding feature of the curve is 
the very marked rise on August 20. Upon examination of the 
rate of evaporation, it will be at once evident that the evaporating 
power of the air was very low throughout. Two plants of this 
