646 TEXTBOOK OF BOTANY 



ending tenninally in a spore-bearing capsule. At the basal end of the 

 leafy stem, many-celled branching rhizoids, seldom more than a few 

 millimeters long, penetrate tlie soil or other substrate. 



Mosses multiply freely by vegetative propagation. On culture media 

 new individuals may develop from nearly any fragment of the plant. In 

 many species small buds occur on stems, and when they become de- 

 tached new indi\'iduals develop from each of them. More speciahzed 

 propagative buds, called "brood bodies," occur abundantly on leaves, 

 stems, and even rhizoids of some species. \^egetative multiplication by 

 fragmentation of the protonema appears almost limitless, especially if 

 the protonema is perennial. Adventitious protonemata may develop from 

 almost any part of the plant. 



The filaments of the protonema, except for their small roundish chloro- 

 plasts, are difficult to distinguish from branching filamentous algae. They 

 continue to branch, and soon fonn a thin green mat over the surface of 

 the soil. Numerous buds, or bulbils, form on the branches of the pro- 

 tonema, and rhizoids and leafy branches develop from them. If the buds 

 are numerous, the upright branches develop close together and form 

 dense clusters or cushions. Some species have an extensive perennial 

 felt-like protonema that completely covers the soil surface, but the up- 

 risht shoots are small and scattered. 



When the spores formed in the capsule of the leafless stalk fall upon 

 soil or other moist substrates, they geiTninate, and from each of them a 

 new protonema develops. These spores constitute a definite stage in the 

 life cycle of a moss plant, which consists of two distinct phases. One 

 phase ends with the development of spores; the other, with the develop- 

 ment of gametes, and fertilization. 



The gametophvte phase and sexual reproduction. The commonly ob- 

 served moss plant composed of protonema, leafy branches, and rhizoids 

 is the gamete-bearing phase, or gametophyte. At the apex of the green 

 leafy stems there appear tufted heads of leaves enclosing groups of 

 slender flask-shaped egg cases, called archegonia (sing, archegonium) . 

 An archegonium ordinarily contains one egg cell and is analogous to the 

 oogonium of the algae, but differs from it in being a multicellular struc- 

 ture (Fig. 298). Antheridia also develop at the apex of leafy stems, 

 sometimes in the same head with the archegonia, and sometimes alone 

 on other stem tips. They may also develop singly or in pairs in the axils 

 of leaves. They are multicellular, and many spenns develop in each of 



