708 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fig. 400 ^^ In Gyathea (figs. 400 !"■ ^^^ ^^) the indusium is cup-like, and closed 

 until the spores are ripe. In BicJcsonia 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 of the sorus. Of 

 CyatheacesB about 200 species are known. 



Fig. 401.— Life-history of a Tern. 



1 A Fern-prothallium seen from the under side. 2 An arehegonium in longitudinal section, s An antheridium * Escape of 



spei™ato.oids from antheridium 5 Young sporophyte with first leaf arising from the prothallium. s complete sporo- 



vnr/nJh! r"" ^"'"-r™""- ^"^^^ ^^'^"^ °' """"'^ °' ^™^' *°™s "°^=" ^^n ^na l^td-al indusia. s A 

 young prothalhum arismg from a spore ; the spore is below. ' natural size ; ' X 8 ; =, a, 4 x 860 ; « x 6 ; ' x 3 ; s x 240. 



Gleiche7iiacece.—M.oaily tropical forms. The sporangia have a transverse annu- 

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

 (of. 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. 



