26 



EXPERIMENTAL PLANT PHYSIOLOGY. 



By means of weights on the other pan equalize the balance. In an 

 hour it will be noted that the end of the scale holding the plant has 

 risen. Take weights from the other pan until the equipoise is restored. 

 The amount of the weights taken off will represent water transpired 

 by the plant. After balancing cover the plant by means of a bell- 



FIG. 24. 



Estimation of amount of transpiration by weighing. (After Oels.) 



jar. In an hour remove the bell-jar, quickly wipe from the pan the 

 water which may have condensed and run down the sides of the 

 bell-jar, and again take off weights to balance. The amount lost 

 will be less than before. The air in the bell-jar soon becomes satu- 

 rated with water and checks transpiration. (Fig. 24.) 



EXPERIMENT 30. 



INFLUENCE OF EPIDERMIS ON TRANSPIRATION. 



Select two Apples and two Potatoes of equal size. Peel one of 

 of each. Weigh and set aside for three hours. Again weigh. It 

 will be seen that a waxy or corky epidermis retards transpiration 

 very efficiently. 



20. Wilting. If the amount of water transpired exceeds 

 that absorbed by the roots, wilting results. This may occur 

 from the destruction of the root-hairs or from an insufficient 

 supply of water in the soil. In the transplantation of trees the 

 branches are trimmed in order that the transpiring surface 

 may be reduced in proportion to the absorbing surface. The 

 latter in the root-hairs is nearly all destroyed by transplan- 



