140 PLANT-LIFE 



that the Mosses have been derived from Liverwort-like 

 forms by mutations and natural selection. This is not 

 easily demonstrable in the present state of our know- 

 ledge; but should such be the case, we may regard the 

 Sphagnaceae as forms intermediate between the ancestral 

 Liverwort forms and the higher Mosses. The latter are 

 a well-defined group, highly specialized according to 

 their rank, and thoroughly fixed in their structure ; they 

 do not seem to lead to higher plants. They are another 

 instance of a natural cul-de-sac, and, so to say, the last 

 word of Nature in their particluar line of development. 



Andreceacece. Includes one genus, Andrecea, with few 

 species, forming a link between the Sphagnums and the 

 Bryacese. These Mosses are of small size, and their 

 colour is very dark ; they may be deep brown, and even 

 blackish. They are among the first plant colonists of 

 newly exposed rock-surfaces, to which they adhere, 

 with much tenacity, by means of well-developed rhizoids. 

 Their spore-capsules burst in a manner peculiar to the 

 Order. Instead of throwing off an operculum, or lid } 

 they split vertically, four slits being formed which do 

 not reach the apex. The stems form branches; the 

 leaves in some species have midribs. The sexes are 

 represented on different branches. 



Bryacece. This Order embraces the great majority of 

 Mosses; the genera are numerous, and we have not 

 sufficient space to describe them here. The reader will 

 already have learned some points of the Order from our 

 study of Funaria hygrometrica. However, attention 

 should be drawn to the protonema in the Bryacese ; with 

 very few exceptions it is filamentous, as described on 

 p. 137, and in this respect these Mosses jseem to be much 



