DETERMINATION OF AMOUNT OF TRANSPIRATION 207 



a direct comparison of the influence of light and darkness may 

 be made. 



279. Determination of Amount of Transpiration by a Potometer. 

 If the negative pressure in a plant is equalized the amount of 



Fig. 105. Determination of amount of transpiration by Anderson automatic balance. 

 The loss of weight of the plant is-equalized by weights, which are added and recorded 

 automatically. 



water taken up in any given time, is a fair equivalent of the amount 

 of transpiration during the same period. It is possible to make 

 much more accurate measurements of the water taken in than 

 that given off, by ordinary methods, and the potometer is perhaps 

 the most useful instrument in studying transpiration. The fol- 



