382 



MOSSES AND FERNS 



CHAP. 



ence' in other respects it is not likely that Hymenophyllum dif- 

 fers essentially from the latter. The sorus occupies the free 

 end of a vein, which often continues to grow for a long time 

 in Trichomanes, and forms a long slender placenta or colum- 

 ella, upon which the sporangia arise basipetally. While the 



FIG. 221. Trichomanes cyrtotheca. Development of the sporangium, X22$. A, 

 Longitudinal section of very young receptacle with the first sporangia (sp) ; B-D, 

 successive stages of development seen in longitudinal section; F, horizontal section 

 of nearly ripe sporangium; r, the annulus. 



receptacle is still very young the tissue of the leaf immediately 

 about it forms a ring-shaped ridge, which grows up in the form 

 of a cup-shaped indusium, which either remains as a tube 



