TRUE MOSSES (BRYALES) 421 
cycle as shown in Figure 376. The Alga-like filament called 
protonema is comparable to the thallus of the Marchantias, and 
the leafy plants to the gametophores. Although the leafy plants 
or gametophores of Moss are not all of the gametophyte, they are 
the conspicuous part of it, the protonemas being microscopic in 
size. One protonema may produce many buds, and, therefore, 
many gametophores. 
In Moss the two generations are more noticeable than in the 
Liverworts. The gametophytes with their leafy gametophores 
present more differentiation than is the rule among Liverworts. 
Fic. 376.— Diagram of the life cycle of Moss. p, protonemas from 
which the gametophores (g) have arisen; a and 6, the sex organs with a 
sperm shown passing from antheridium to archegonium; c sporophyte which 
the fertilized egg produces; s, spores which grow new protonemas and thus 
the life cycle is completed. 
The sporophyte, consisting of a large sporangium supported on a 
long stalk, or seta, is usually quite conspicuous. It is more multi- 
cellular and has carried the sterilization of sporogenous tissue 
farther than the sporophytes of most Liverworts have. Not 
only is it larger and more multicellular, but it also shows more 
differentiation than the sporophytes of Liverworts. The seta 
is so differentiated as to have a central strand of elongated 
cells for conduction. The sporangium of the Moss sporophyte 
develops at its top a special lid-like structure (operculum) for 
opening, and often special tooth-like structures (peristome) are 
produced just under the lid and assist in scattering the spores. 
