TBANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



89 



It has long been known from the work of Comes^ that the sum of 

 the transpiration of the lower leaf surface alone and the upper surface 

 alone is greater than the rate from a normal uncoated leaf. I am able 

 to confirm this, as may be seen by comparison of D and E in table 34, 

 indicating an average increase of 34 per cent in top alone plus bottom 

 alone over the uncoated leaf, in Diplazium (see fig. 13). I have taken 

 for granted that the amounts by which the transpiration of top alone 

 and bottom alone are increased by coating the opposed surface are 

 proportional to the normal rates themselves, an assumption which can 

 not be far from the truth. On this assumption I have divided the 

 amounts of transpiration in the uncoated plant, hour by hour, into 

 two amounts, which are proportional to the amounts of water loss from 

 the top alone and the bottom alone in the coated plants. This calcu- 

 lation gives the approximate amounts of transpiration for the top and 

 the bottom of an uncoated leaf (G in table 34), hour by hour. As the 

 degree of cutinization is ahke on the two sides of the leaves of the plants 

 used, and as the epidermal walls are of almost the same thickness 

 on the two sides, the cuticular transpiration of the bottom of the leaf, the 

 stomata eliminated, is practically the same as that of the top of the leaf. 

 The total area occupied by the stomata is so small as to be practically 

 negligible. The actual stomatal transpiration is, therefore, the differ- 

 ence between the calculated transpiration amounts for the upper and 

 lower leaf surfaces (H, table 34), The values for true stomatal trans- 



Table 34. — Showing method used to determine actual stomatal and cuticidar transpiration. 

 Diplazium celtidifolium. (Based on data given in table 33.) 



^Comes O. Azione della temperatura, della umidita relativa et della luce suUa transpiratione 

 dello piant'e. ' Rendic. d. R. Acad. d. Science di NapoU. 1878. 



