CH. XXIX] 



THYRSOPTERIDEAE 



261 



of spores is 48 to 64. The parent-cell of the sporangium is not uniform in 

 shape: it commonly has a square base, and the first segment-wall passes 

 obliquely to the basal wall as in Schizaeaceae, the second being inserted 



Fig. 527. Thyrsopteris elegans Kze. ^=part of a leaf, above a sterile, and belo\\- a fertile pinna. 

 i? = part of a sterile pinnule. C=part of a fertile pinnule. Z' = sorus with indusium. A" = sorus 

 with the indusium cut through. /^= sporangium. (After Kunze, from Engler and Pranll.) 



obliquely on the first {A, C). The result is that the stalk is short and thick. 

 Sometimes the parent-cell is wedge-shaped {E). Thus Thyrsopteris wavers 

 between a more primitive and a more advanced type of segmentation of the 

 sporangium. The orientation of the sporangia is usually as in the Hymeno- 



