ALTERNATION OF GENERATIONS 243 
421. Mossworts may then be described as green plants 
in which the gametophyte is a prostrate or erect some- 
what long-lived plant, producing antherids, and oogones 
(the latter enclosed in archegones). After fertilization a 
distinct structure, the sporophyte, is produced, but al- 
though it rests on and in the gametophyte and obtains its 
supply of water and much of its food from it there is 
no organic connection between them. In this sporo- 
phyte certain internal cells (the “spore mother-cells’’) 
divide twice and thus produce internally four spores 
each. These eventually germinate and produce other 
gametophytes. 
422. Here it should be noted that the nuclei of the 
gametophyte cells contain a definite number of chromo- 
somes, and that on the fertilization of the egg this number 
is doubled. This double number is maintained in the 
sporophyte until spores are formed by division into fours, 
at which time a reduction takes place to the original num- 
ber. Soin this phylum the two generations are separable 
also by their chromosome numbers in addition to the 
other more obvious differences. 
423. ‘The antherids are complex structures. They are 
usually short-stalked, and consist of a layer of large 
boundary cells within which are very numerous, small, 
more or less cubical cells, each of which produces in- 
ternally an elongated, more or less spiral, biciliate sperm. 
The walls of these spermatogenous cells dissolve, leaving 
the sperms free within the cavity of the antherid. By the 
rupture of the apical cells the sperms escape. This 
occurs only when the antherid is covered with water (rain, 
dew, etc.). | 
424. The archegone is a flask-shaped, elongated organ, 
consisting of an enlarged lower part (venter) containing 
the egg, above which is the slender neck, at first closed at 
