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- 



