MOSSES AND LIVERWORTS (BRYOPHYTES) 259 



divide by oblique walls, and form buds (Fig. 214, A, I). These 

 buds continue to grow, the outermost cells develop leaves, the 

 central ones become the stem, and from the 

 lower ones root-like hairs (rhizoids) descend 

 into the soil (Fig. 214, B, I). The buds, there- 

 fore, are the beginnings of the leafy moss 

 plant (Figs. 215 and 216). Young buds may 

 grow directly into leafy plants, or become 

 dormant for a time and then 

 resume their growth. Since 

 the alga-like growth is that 

 which precedes and produces 

 the leafy moss plant, it is 

 called the protonema^ mean- 

 ing " primitive thread." 



243. The moss plant: nu- 

 trition. Dense growths of 

 moss plants may form from 

 a single mat of protonema. 

 The rhizoids, embedded in soil, humus, or de- 

 caying timber, bring these plants into close 

 relation with the water supply. The whole 

 dense growth may serve as a sponge, so that 

 the plants may then be virtually immersed 

 in water. Some mosses really live part or 

 all of the time in streams or bodies of still 

 water. In exposed regions mats of moss may 

 become dry enough to crumble into powder 

 when handled, but, if undisturbed, may pro- 

 ceed with their growth upon the return of 

 moisture. Some mosses also show remark- 

 able ability to withstand extremes of heat 

 and cold. 



The stem and leaf arrangement that exists in the mosses 

 exposes chlorophyll to the light in a different way from that 

 which was found in the algae. With the leaves arranged 



FIG. 215. A fully 



formed leafy moss 



plant 



I, leaves; s,stem; r, 



rhizoids. Ten times 



natural size 



FIG. 216. A leafy 

 moss plant upon 

 which the sporo- 

 phyte has grown 



l.p , the leafy plant ; 



s, seta; c, capsule. 



Five times natural 



size 



