7Q8 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fig 400 13 In Cyathea (figs. 400 10 ' 11 ' 12 ) 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 of the sorus. 

 Cyatheacese about 200 species are known. 



Fig. 401. Life-history of a Fern. 



i A Fern-prothallium seen from the under side. 2 An archegonium in longitudinal section. An antheridium. * Escape of 

 spermatozoids from antheridium. * Young sporophyte with first leaf arising from the prothallium. Complete sporo- 

 phyte of Asplenium Ruta-muraria. 7 Under surface of pinnule of same, showing linear sori and lateral indusia. 8 A 

 young prothallium arising from a spore ; the spore is below. natural size ; 1 x 8 ; 2 , 8 , * x 350 ; 6 X 6; 7 x 3 ; 8 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 6 , and 400 9 ). 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. 



