CHAPTER VI 



THE BRYALES 



Under the name Bryales may be included all the other Mosses ; 

 for although the so-called cleistocarpous forms are sometimes 

 separated from the stegocarpous Mosses as a special order, the 

 Phascaceae, the exact correspondence in the development of 

 both the gametophyte and sporophyte shows that the two groups 

 are most closely allied, the former being either rudimentary or 

 degraded forms of the others. 



With few exceptions the protonema is filamentous and 

 shows branches of two kinds, the ordinary green ones with 

 straight transverse septa, and the brown-walled rhizoids with 

 strongly oblique ones, but the two forms merge insensibly into 

 one another, and are mutually convertible. In a few forms, 

 notably the genus Tetraphis, the protonema is thalloid, and as 

 in Sphagnum these flat thalli give rise to filamentous proto- 

 nemal threads, which in turn may produce secondary thalloid 

 protonemata. The genus Diphyscium (C. Muller (3), pp. 

 169, 170), develops upon the protonema solid, trumpet-shaped 

 bodies. In some of the simpler forms, e. g., Ephemerum, the 

 protonema is permanent, and the leafy buds appear as append- 

 ages of it ; but in most of the larger Mosses the primary proto- 

 nema only lives long enough to produce the first leafy axes, 

 which later give rise to others by branching, or else by second- 

 ary protonemal filaments growing from the basal rhizoids. 

 The early stages of development of the primary protonema are 

 easily traced, as the spores of most Mosses germinate readily 

 when placed upon a moist substratum. The ripe spores usually 

 contain abundant chlorophyll and oil, and the thin exospore is 

 brown in colour. The spore absorbs water and begins to en- 

 large until the exospore is burst, when the endospore protrudes 



188 



