404 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. Ftrst, 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 thallus 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, aérenchyma, 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. 
