110 THE PLANT 
check. Two plants of Helianthus annuus were taken from the pots in which 
they had grown, and the soil was carefully washed from the roots. Each 
plant was weighed with its roots in a dish of water to prevent wilting, 
and then carefully potted, one in each battery jar. A thistle tube was placed 
in the soil of each jar to facilitate aeration, as well as the addition of 
weighed amounts of water, when necessary, and the rubber cloth attached 
in the usual manner to prevent evaporation. The entire outfit was weighed 
again, and the weighing repeated at 8:00 A.M. and 5:00 P.M. for five days, 
in order to determine the amount of transpiration and its relation to the 
water absorbed. The plants were kept in diffuse light to prevent excessive 
water loss while the roots were becoming established. At the close of the 
experiment, the jar and its contents were weighed finally. The plants were 
removed and weighed, the soil particles being shaken from the roots into 
the jar, which was also weighed. The results obtained were as follows: 
Wt. of pot . £0 ab- |72O tran- 
and dry coil Wt. of pot and wet soil | Total 420 | 20 left|" oon eg spired 
T —_Ir 
I 1846.0 g. | 22180g. | 2174.3 ¢, 372.0 g. | 3283g.| 43.7g.| 43.7¢. 
Il 1886.7 g. | 22532¢ | 22916 g. 366.5 g. | 334.9¢.| 316¢.| 316g. 
The amount of water absorbed may be obtained directly by subtracting the 
final weight of the jar and moist soil from their first weight, but a desirable 
check is obtained by taking the dry weight of jar and soil from the first, 
and the final weight of these, and subtracting the one from the other as 
indicated in the table. A second check is afforded by daily weighings, 
from which the amount of water transpired is determined. Since the two 
sunflower plants made practically no growth during the period of experi- 
ment, the exact correspondence between water absorbed and water lost is 
not startling, though it can-not be expected that the results will always 
coincide. 
This method has certain slight sources of error, all of which, it is thought, 
have been corrected in a new and more complete series of experiments 
now being carried on. The aeration of the soil is not entirely normal, as is 
also true of the capillary movements of the water, on account of the non- 
porous glass jar and the rubber cloth. Since the latter are necessary condi- 
tions of all accurate methods for measuring absorption and transpiration, 
the resulting error must be ignored. It can be reduced, however, by forcing 
air through the thistle tube from time to time. Sturdy plants, such as the 
sunflower, are the most satisfactory, since they recover more quickly from 
the shock of transplanting. Almost any plant can be used, however, if 
