74. 



occurs at the margin. 



If v/e regard the increase in size of the cells 

 after the introduction of v/ater as aji index of their capacity 

 to lose water during drying, it tecomes evident that the 

 cells of the upper epidermis at the leaf margin must lose 

 least water, while those of the midrib region must lose most* 

 The lo\7er epidermal cells of the midrib region, however, lose 

 less water than the upper epidermal cells of the same region. 

 It is further evident that the greatest decrease in size, under 

 dry conditions, in all the cells measured^is that in width. 

 It thus appears that the curling of the leaf is caused chiefly 

 by the unequal ra,te of water^loss of the cells of the different 

 parts of the leaf. 



Physiological Significance of the Scales 



The presence of the scales on the lower surface 

 of the polypody suggests its possible function a> a 

 protection against dessication, According to ICarsten (14) 

 the scales present on the underside of the stem of Polyp odium 

 imbrioatam serve to distribute the water drops which settle 

 on the stem. In Poly podium sinuosum.h ov/ever. the scales ser"W« 

 for absorbing water which appears on the stem in the form of 

 drops,Schimper (25) and Mez (18) both attribute the function 

 of water absorption in Tillandsia to the scales, Mez regards 

 the mechanism by which the water is absorbed by the scale as 

 either osmotic or capillary, So far as the writer knows the 

 function of the scales in P. polypodioides has not been detBB- 

 mined, Although in a number of sections of dry leaves the v/ing 



