81. 



VI.HISTOLOGIGAI. STUDIES 



A study of ths structure of the root and of the root 

 hairs of P. polypodioides show first of all no siyns of 

 mycorrhizal association, The stucture of the root as whole 

 seems to present the appearance of a typical fern root, though 

 the root hairs differ somewhat from the ordinary type, Instead 

 of being more or less uniform in thixjkness as root hairs 

 generally are, these are swollen or "bulbous at the base and 

 taper off to a more or less blunt point at the tip (Figs«25Jkui.d 



It will be v/ell to describe the development and mature 

 structure of the scales of the leaf of this epiphytic polypody 



since this knowledge should aid in solving the problem of 

 their function, A sagittal section of a very young leaf of 

 a mature plant, or of a young sporophyte, reveals the fa6t that 

 each scale arises from an epidermal cell, The scale is, of course 

 initiated very close to the grov/ing point of the leaf. The 

 epidermal cell from which the scale arises first divides by 

 a transverse wall which thus forms two cells, an. inner cell 

 and outer one, The inner cell remains on the level with the 

 epidermal cells, v/hile the outer one buldges out and soon 

 divides by a second transverse v/all forming again an inner 

 cell and an outer cell, The oi/ter of these two cells continues 

 to divide several times forming a plate of cells, while the 

 lower cell by several successive transverse and one median 

 longitudinal division, gives rise to the stalk of tie scale. 

 The cells of the plate grow out more rapidly towards the 

 growing point of the leaf so that in the mature scale the 



