372 MOSSES AND FERNS chap. 



and in Lygodiuin, Prantl -^ states that they form but a single 

 row. He also says that the roots are always diarch, like the 

 Polypodiaceae, but gives no further details of their growth or 

 structure. 



TJie Sporangia 



The development of the sporangia has been carefully in- 

 vestigated by Prantl," and in origin and arrangement they 

 differ decidedly from the other Leptosporangiates, but approach 

 most nearly Osvtunda, and among the eusporangiate Ferns 

 show a certain likeness to Botrychium. The sporangia arise 

 always in acropetal order from the apex of the terminal seg- 

 ments (sorophore) of the sporophyll, and are strictly lateral in 

 origin, not originating from epidermal cells, but from marginal 

 ones. The young sporangium appears as a lateral outgrowth 

 of the margin, exactly like a young pinna upon the main axis, 

 and the young sorophore has the appearance of a young 

 pinnate leaf, and at this stage recalls strongly the similar one 

 in Botrychium. This is especially marked in Aneiviia and 

 Lygodiuvi, less so in Schizcsa, where the sporangia are smaller, 

 and the mother cells project much more strongly. The early 

 divisions correspond closely with those of the Hymenophyllacese, 

 and as there the tapetum is massive and two-layered, and the 

 stalk of the sporangium very short. The wall is derived in 

 major part from the cap cell, which in all the forms becomes 

 much more developed, than in any other Ferns, and from it 

 alone the apical annulus is derived.^ In Aneimia and Mohria 

 the tissue of the tip of the leaf adjacent to the sporangia grows 

 into a continuous indusium, which pushes them under to the 

 lower side. In Lygodium (Fig. 192) each sporangium very 

 evidently corresponds to a single lobe of the leaf segment, and 

 has a vein corresponding to this. The pocket-like indusium 

 surrounding each sporangium grows up about it much as the 

 indusium of Trichoinanes grows up about the whole sorus. 



The CyatheacecB 



These are all Ferns of large size, some of them tree-Ferns, 

 10 metres or more in height. They occur in the tropics of 



1 Prantl (5). 2 Prantl, I.e. 



^ The divisions in the wall are too complicated to be explained without numerous 

 figures. See Prantl's figures, Plates V.-VIII. 



