424 BRYOPHYTES (MOSS PLANTS) 



characteristic of the Bryales, while it has some that belong to 

 neither. It is often called a synthetic form, for it combines the 

 characters of Liverworts and True Mosses. 



Summary of Bryophytes. — The Bryophytes show progress 

 over the Algae in a number of ways. First, the Bryophytes 

 established the land habit, which meant the establishment of a 

 plant body that was adapted to live and function in the air rather 

 than in the water. In establishing the land habit the plant body 

 had to develop tissues to protect against transpiration, sex cells 

 had to be jacketed, and sex organs, now called antheridia and 

 archegonia, consequently became multicellular, and tissues for 

 utilizing the carbon dioxide of the air and sunlight in making food 

 had to be provided. Second, although alternation of generations 

 is quite prominent in some of the higher Algae, it is a very dis- 

 tinct feature throughout the Bryophytes. Both gametophyte 

 and sporophyte generations show considerable advancement 

 from the simplest Liverworts, where the gametophyte is a small 

 flat thaUus and the sporophyte merely a sporangium, to the 

 highest of the Mosses, where there is a leafy gametophore and a 

 sporophyte with a well developed seta and a sporangium having 

 an operculum, peristome, columella, aerenchyma, and food- 

 making tissues. 



It should be noticed, however, that, although the Bryophytes 

 adopted the land habit, they have a swimming sperm which puts 

 a limit on the size of gametophytes, for swimming sperms can 

 travel only short distances and only when water is present. In 

 Mosses and the more complex Liverworts, there is much evidence 

 that a large percentage of the sperms are not able to reach the 

 archegonia. But the spore, since it is protected against drying 

 and can, therefore, be transported by the wind, puts no limit on 

 the size of the sporophyte. This means that the higher plants 

 must consist chiefly of the sporophytic generation. 



