MOSSES AND LIVEKWOETS (BRYOPHYTES) 273 



alternation of generations. In the mosses the two generations 

 are easily observed. There is a gradual development of the 

 sporophyte from the very simple condition in Riccia through 

 many intermediate forms, one of which is Marchantia, to the 

 relatively complex condition in Antlioceros. From an entirely 

 dependent sporophyte which is embedded within the tissues of 

 the gametophyte, such as is seen in Riccia, there is an increase 

 in complexity of the sporophyte until it becomes an upright, 

 chlorophyll-bearing, almost independent structure. Although 

 almost all of the Riccia sporophyte produces spores, the cap- 

 sule is so small that the total number of these spores is not 

 large. As the sporophyte increases in size and becomes more 

 specialized, proportionately less of it is devoted to spore pro- 

 duction, but actually very many more spores are formed, since 

 the whole spore-producing part of the sporophyte is so large. 

 The gametophyte is the chief chlorophyll-working generation 

 in bryophytes, and the sporophyte depends upon it for all or 

 most of its nourishment. Special structures for the perform- 

 ance of nutritive work by the gametophytes exist. These are 

 rhizoids, leaves, and stems. It is worthy of note that in none 

 of the succeeding groups of plants is the gametophyte so well 

 equipped for independent nutritive work as in the bryophytes. 



255. Classification: 



Bryophytes 



Class I. Hepaticae (liverworts). Leading genera used as illustrations, 



Riccia, Marchantia, Antlioceros 



Class II. Musci (mosses). Leading genera used as illustrations, 

 Funaria, Sphagnum, Polytrichum 



