no 



THE PLANT 



check. Two plants of Helianthus anniius 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 

 and dry soil 



Wt. of pot and wet soil 



Total H2O 



mo left 



mo ab- 

 sorbed 



//2O tran- 

 spired 



I 



II 



1846.0 g. 

 1886.7 g. 



2218.0 g. 

 2253.2 2 



II 

 2174.3 

 2221.6 



372.0 g. 

 366.5 g. 



328.3 

 334.9 



43.7 g. 

 31.6 g. 



43.7 g. 

 31.6 g. 



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 



