272 



BOTANY 



Marattiacese are much older than the leptosporangiate Ferns which have now 

 largely superseded them. 



FIG. 238. Dansea alata. A, transverse section of vascular bundle of the petiole 

 (X 175) ; x, tracheary tissue; t, tannin cells. B, cross-section of a mucilage-duct 

 (X175). 



SUBCLASS II. LEPTOSPORANGIATE 



Much the greater number of existing Ferns belong to the second 

 division, the Leptosporangiatse. These are characterized by having 

 the sporangium the derivative usually of a single epidermal cell. 



FIG. 239. Angiopteris evecta. Development of sporangium. A, B, sections of young 

 sporangia. (After GOEBEL.) C, section of a nearly full-grown sporangium, show- 

 ing persistent tapetum, t, and annulus, r (x 75). 



