XLVIIl] 



CYSTOPTERIS 



251 



placenta swells strongly: later, however, it grows more actively and forces the 

 sorus definitely to the lower surface" {R, Fig, 748, C, D). How nearly this 

 corresponds to what is seen in similar sections o{ Diyopteris filix-nias appears 

 on comparison of the drawings of Cystopteris with Fig. 748, E: in both, 



Fig. 747. Cystopteris fragilis (L.) Bernh., pinnule of a 

 form from Tasmania, with its sorus: enlarged. (After 

 Hooker, from Christ.) 



Fig. 748. Development of the sorus of Cj/J/'£'//t?;'«. A, B=- 

 median sections of sori of C. fragilis, showing relation to 

 the margin: /= first sporangium: /«(/. = indusium. C, D = 

 younger states of C. montana, after Von Goebel : I— first 

 sporangium: /W. = indusium : y? = leaf-margin. ^ = a young 

 sorus of Dryopteris Jilix-mas for comparison. (All highly 

 magnified.) 



however, the adult sorus is clearly superficial. The first sporangium (/) is 

 followed by others in gradate sequence. The facts of development of the 

 sorus in Cystopteris thus show a near similarity to those seen in Lindsaya 

 (Chapter XXXVII, Fig. 603), which is held to be a Davallioid derivative: in 

 fact a marginal type. 



