236 



BOTANY 



the operculum, loosened by the destruction of the cells of the annu- 

 lus. After the operculum is thrown off, the peristoine teeth, by their 

 hygroscopic movements, assist in emptying the spores from the 

 theca. The seta also, is often hygroscopic. All of the archespo- 

 rial cells develop spores. The latter are usually small and contain 

 chlorophyll. 



The venter of the archegonium becomes very large in most Mosses, 



FIG. 200. Sphagnum, sp. A, -B, young protonemata 

 (x 200). C, older protonema with leafy bud, k 

 (X 35) ; r, marginal rhizoids. 



FIG. 201. Sphagnum squarrosum. 

 Leafy shoot, with sporophytes, 

 borne at the end of leafless 

 branches (X 2). . 



and forms a bell-shaped calyptra about the slender embryo. Finally 

 it becomes torn away, and is carried up by the elongating sporophyte, 

 whose summit is protected for a long time by this conspicuous mem- 

 branaceous cap. 



Classification of the Musci 



The Musci may be divided into three orders, Sphagnales, An- 

 dreseales, and Bryales, of which the latter comprises an over- 

 whelming majority of existing Mosses. 



