708 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fig. 400 ^^ In Cyathea (figs. 400 ^''•^^■^2) 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. Of 

 Cyatheaceae about 200 species are known. 



Fig. 401.— Life-history of a Fern. 



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

 spermatozoids from antheridium. s Young sporophyte with first leaf arising from the protlialliuni. « Complete sporo- 

 phyte of Asplenium Jiuta-muraria. ' Under surface of pinnule of same, showing linear sori and lateral indusia. « A 

 young prothallium arising from a spore ; the spore is below. « natural size ; i x 8 ; 2, s, 4 x 350 ; « x 6 ; ' x 3 ; * 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 

 (c/. 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. 



