61. 



curling upv/ard and inward of the margins of each pinna towards 

 its midrib, The folding of the individual pinnae is soon 

 followed by the curling of each leaf and v/hile this takes 

 place the rachis begins to twist and to curl, Thus, in all cases, 

 the curling of the leaf causes the upper epidermis to be hidden 

 from the outside, while the lower epidermis, v;hich is covered 

 with numerous 3CpJ.es, remains exposed.This chsjcacteristic curling 

 whic/^ conceals the upper surface and leaves only the lower surface, 

 exposed, suggests at once that this is an adaptation of the 

 leaf to xerophytic conditions.lt might be assumed from such 

 a behavior of the leaf that its upper epidermis loses v/ater 

 more readily than its lower one, and by being rolled in when 

 the air is dry the leaf avoids the danger of excessive 

 transpiration from the upper surf ace. The scales which cover 

 the lower surface of the leaf might well be assumed to function 

 as an aid in lessening the evaporation from the lower epidermis. 

 To determine definitely whether these assumptions are correct 

 and to learn which side of the leaf really loses the greater 

 amount of v/ater under given conditions, experiments were 

 carried on in the laboratory both on living and dead leaves of 

 the epiihytic fern, Abundant material for these experiments 

 was obtained from Mississippi through the kindness of Professor 

 J»M,Beal and a large clump of the living fern vf&s sent from 

 Athens, Ga, by Professor J,M,Reade to both of who the writer 

 here expresses his sincere thanks. 



