224 



THE SPORE-PRODUCING ORGANS 



[CH. 



Pig. 2IQ. Sections vertically through the margins of young pinnules of Histiopteris incisa, showing 

 the relation of soral origin to the marginal segmentation. J? = receptacle; .S— sporangium; F—'m- 

 dusial flap. It is seen that the receptacle is close to the margin in A, B, but definitely superficial 

 in Z). ( X 200.) 



Fig. 220. A, j9 = vertical sections through young sori of Pteris serrulata. (x 150.) 6'=similar 

 section through a nearly mature sorus of Pieris cretica. ( x 75.) The indusium is here a direct 

 continuation of the marginal growth, and the flattened receptacle and sporangia arise from the 

 lower surface. 



