MOSSES AND LIVERWORTS. 129 



liverworts in habit, but the group as a whole is charac- 

 terized by a manifest differentiation into root, stem, and leaf, 

 and by a somewhat more complicated fructification. The 

 capsule, with its seta, calyptra, operculum, and peristome, 

 differs widely in different genera, but is so far character- 

 istic as to mark at once the relationship of the plant to 

 which it belongs. 



Mosses and liverworts, however, are so manifestly re^ 

 lated to each other as to necessitate their grouping in a 

 common class. This class is specially charac- oycleof 

 terized by the cycle of development, which is development, 

 essentially the same in both of the groups of which it is 

 composed. From the spore proceeds, in germination, a 

 vegetative growth, the protonema, from which arises after- 

 wards the leafy plant. On this are borne the organs of 

 reproduction. From the fertilized oosphere arises the 

 sporophyte, and with the production of spores the cycle is 

 completed. There is, perhaps, no group of plants in which 

 this " alternation of generations " is more sharply defined 

 than in the mosses. By simply pulling out the seta with 

 the capsule from the stem that supports them, the sporo- 

 phyte, or non-sexual generation, is mechanically separated 

 from the obphyte, or sexual generation. The student is 

 advised to actually perform the operation, and .to dwell on 

 the fact involved, and the language by which it is ex- 

 pressed, until the alternation of generations is seen to be a 

 real part of the history of the plant, and not merely a 

 theoretical conception. In our general review of crypto- 

 gams, we shall have occasion to compare this with what 

 takes place in other groups. 



