TKANSPIEATION BEHAVIOR OF RAIN-FOREST PLANTS- 



87 



relative amounts of transpiring surface per unit volume in desert and 

 rain-forest plants is, of course, profoundly concerned in the determina- 

 tion of the absolute amounts of water lost by plant individuals. The 

 prevalent conception that plant transpiration is reduced in desert plants 

 arises from a consideration of the reduced transpiring surface of desert 

 plants rather than from a knowledge of their water loss per unit area 

 as compared with hygrophilous plants. 



Table 33. — Influence on transpiration exerted by coating upper or lower leaf surfaces. 



Series run in laboratory, with three individuals of Diplazium celtidifolium, by weighing 

 method. First group of readings on uncoated plants, second on plants coated as indicated. 

 Leaf areas: (top and bottom): A, 222.6 sq. cm.; B, 227.1 sq. cm.; C, 181.9 sq. cm. 



RELATIVE AMOUNTS OF STOMATAL AND CUTICULAR 

 TRANSPIRATION. 



The thinness of epidermal wall and lightness of cutinization which 

 are well known to characterize rain-forest plants made it seem desirable 

 to differentiate between stomatal and cuticular transpiration and to 

 attempt an estimation of their comparative amounts. In the lack of a 

 direct method of differentiating between the stomatal water loss and that 

 from the epidermis of both upper and lower leaf surfaces, the following 

 indirect means of obtaining approximate values for them was employed. 



Three potted plants of the same species were run simultaneously in 

 order to obtain a calibration of their rates of transpiration with respect 

 to each other. After being run together through one day, the upper 



