708 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fig. 400^^. In Cyathea (figs. 400^"' ^^' ^'^) the indusium is cup-like, and closed 

 until the spores are ripe. In Dicksonia the sorus is marginal, with bivalved indu- 

 sium; in Alsophila the sori are scattered, and the indusium absent or rudimentary; 

 in Hemitelia the indusium is scale-like, and situated on one side ot" the sorus. Of 

 Cyatheaceae about 200 species are known. 



Fig. 401.— Life-history of a Fern. 



1 A Fern-prothallium seen from tlie under side. ^ An archegouium in longitudinal section. 3 An antheiidium. * Escape of 

 sperniatozoids from antlieridium. s Young sporopliyte with first leaf arising from the prothallium. '■ Coiuplete sporo- 

 phyte of Agplenium Ruta-muraria. 7 Under surface of pinimle of same, showing linear sori and lateral indusia. » A 

 young prothallium arising from a spore ; the spore is below. « natural size; i x S; 2, s^ 4 x 350; s x G; ' x 3; s x 240. 



Gleicheniacece. — Mostly tropical forms. The sporangia have a transverse annu- 

 lus, and are collected into little sori of 3 or 4 sporangia, often very closely packed 

 (cf. figs. 400 ^ and 400 ^). The frond usually forks repeatedly. There is only one 

 genus, Gleichenia, which has some 40 species. 



Schizceacece. — The members of this family are also for the most part tropical. 



