304 THE BRYOPHYTES 



the fruit, alternates with the sexual generation, or gametophyte, 

 and is always attached to it and dependent upon it for water 

 and, at least in large part, for certain foods. The asexual spores 

 produced by the sporophyte are of a new type not found in the 

 thallophytes. 



The two classes of the Bryophyta are distinguished by the 

 following characters : 



Class I. The liverworts, or Hepaticce. This class is character- 

 ized by relatively simple sporophytes (Anthoceros excepted). 

 The gametophytes are thalloid except in the leafy liverworts, 

 and have distinct upper and lower surfaces (dorsiventral 

 symmetry). 



Class II. The mosses, or Musci. These have relatively com- 

 plex sporophytes, whose spore' cases open by covers, and the 

 rim of the spore case is frequently fringed by a circle of teeth. 

 The gametophytes have erect leafy stems, and the leaves are 

 generally arranged spirally (radial symmetry). 



301. Summary of the thallophytes. The sexual organs are 

 almost always one-celled structures. The chief exceptions are 

 the so-called plurilocular sporangia of the brown alga3 (Sec. 235) 

 and the peculiar antheridium of the stoneworts (Sec. 230). 

 There is no organ in the thallophytes resembling the archegonium 

 in structure or development. There is no alternation of sexual 

 generations with asexual in most of the thallophytes. However, 

 in the red algse (Rhodophycece) and the sac fungi (Ascomycetes) 

 the fertilized female cell produces peculiar fructifications called 

 cystocarps and ascocarps, which develop asexual spores and 

 constitute phases in the life history, alternating with the sexual 

 plants. These phases are sporophytes, and there is a true alter- 

 nation of generations in the red algse and sac fungi, but these 

 structures are peculiar and are believed to be independent de- 

 velopments in these two remarkable groups and not related to 

 the sporophytes of the bryophytes. None of the thallophytes 

 have sexual plants resembling in detail those of the liverworts or 

 mosses. The plant body is generally a thallus, though the variety 



