708 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fig. 400 1». In Cyathea (figs. 400i''.»'i2) the indusium is cup-like, and closed 

 until the spores are ripe. In Bicksonia 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 

 Cyatheacese about 200 species are known. 



Fig. 401.— Life-history of a Fern. 



1 A Fem-prothallium seen from the under side. ^ An archegonium in longitudinal section. ' An antheridium. * Escape of 

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

 phyte of Agplenium Ruta-muraria. ? Under surface of pinnule of same, showing linear sori and lateral indusia. ^ X 

 yoting protliallium arising from a spore ; the spore is below. * natural size ; » x S ; 2, », < x 350 ; * x 6 ; ' X S ; 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 

 (c/ figs. 400 ®, and 400 ^). The frond usually forks repeatedly. There is only one 

 genus, Gleichenia, which has some 40 species. 



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



