104 A MOSS PLANT. 



form structures not unlike the moss protonema, but al- 

 most directly they pass into the dorsiventral liverwort 

 body. In the true mosses the protonema may persist 

 for a long time before giving rise to a leafy shoot. But 

 this phase of the gametophyte is purely vegetative, since 

 it produces no sexual organs and consequently cannot 

 produce a sporophyte. It may branch and extend 

 itself, thereby increasing in vigor and probability of 

 producing more than one leafy axis. It may also serve 

 to carry the plant through unfavorable periods. 



With the development of the leafy shoot from the 

 buds on the protonema, there appear structures not 

 equalled in complexity by the gametophytes of the liver- 

 worts. The upright stem supports a system of leaves 

 that are radially arranged, thereby exposing the chlorophyll 

 to the light in a better way than has yet been done. At 

 the lower end of the stem are anchoring organs, the 

 rhizoids. It may be that these absorb materials from 

 the earth and carry them to the stem, through which by 

 means of specialized tissues they may be transported 

 to the leaves. The stem is almost entirely relieved of 

 chlorophyll work and is given over mainly to the work 

 of support, its form and structure being adapted to this 

 function. The leaves show distinctly differentiated con- 

 ducting tissues, which also help stiffen the leaf. The 

 margin of the leaf is also strengthened in some cases. 



The sexual organs are borne at the apex of the gameto- 

 phyte stalk and are more or less enclosed by the paraphyses 

 that grow among them. Mosses may be monoecious or 

 dioecious. The oospore begins its development within 

 the venter of the archegonium, and its growth stimulates 



