TRUE MOSSES (BR Y ALES) 



421 



cycle as shown in Figure 376. The Alga-Hke 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. 



Fig. 376. — Diagram of the life cycle of Moss, p, protonemas from 

 which the gametophores (g) have arisen; a and b, the sex organs with a 

 sperm shown passmg 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. 



