CUTICLES OP CYCADEAIN' FEONDS. 



159 



are more regularly rectangular (text-fig. Ij. Over the lateral veins also the cells are 

 somewhat rectansjular, narrow, and elono^ated, hut the walls are undulate. At the 



the cells gradually become smaller and straight-walled. 



According to 



pinna-margins 



Kraus the cell-walls are unequally thickened, more secondary material being laid down 

 on the outer side of a bend than the inner. Very little difference was noted in the 

 present case, perhaps owing to the comparative thinness of the walls ; and after careful 

 preparation and staining, it seemed as if the slight inequality might be due to optical 

 effect rather than to any real difference in the amount of thickening. 



Fig. 1. 



Stangeria paradom : surface view of the cuticle from the midrib of the upper side of the leaf, 



showing a stoma with characteristic thickening due to the dorsal ((^) and ventral (v) liguified 

 lamellae of the guard-cells ; g, the raised polar ends of the guard-cells. Note the absence 

 of folds of the cutin in the neighbourhood of the stoma, x 450. 



Stomata occur scattered and irregularly-placed with regard to the pinna 

 lower side of the lamina ; they are generally absent in the very narrow^ ar 

 lateral veins. They occur on both upper and lower mid-rib areas, their ' 



tho 



parallel with that of the pinna (text-fi 



The upper, as well 



the lower stomata 



appear to be functional, as there 'is a well -developed air-space underlying each 



the level of the epideruiis (PI. 17. figs. 1 & 5) 



the 



havin 



The stomata lie practically 

 guard-cells are not sunk as in 



Each stoma is surrounded by from four to six epidermal 



straighter walls than the rest of the epidermis. These » subsidiary cells ' are particularly 

 marked in the case of the lower stomata, and 



the case of Zamia (of. PL 17. fig. 5 with PL 18. fig. 13) 



J slightly thinner 



and lateral cells : PL 17. fig. 1 sho\\ 

 Subsidiary cells. 



an 



polar 

 example with two polar and two lateral 



may usually be distinguished 



Division of the lateral cells often takes place, as text-fig. 1 show 



