[Chap. XLVIII MOSSES AND LIVERWORTS 645 



In moist, shaded habitats various small salamanders, insects, snails, 

 worms, fungi, bacteria, and algae live with the bryophytes as a miniature 

 microcosm. From the plants, both living and dead, the animals secure 

 food, cover, and a more continuous water supply. The saprophytic fungi 

 simply grow through the mass of liverworts and mosses and become in- 

 terlaced with them. Some of the fungi, however, are wholly or partially 

 parasitic, and live on and within the bryophyte cells. Certain species of 

 aerial and terrestrial algae as well as various soil bacteria are also sure 

 to be found in the community. The commonest example of an alga living 

 within liverworts is the blue-green Nostoc in cavities of the two liver- 

 worts, Anthoceros and Blasia. 



The economic and biological importance of the bryophytes is much 

 less than that of either the algae or the fungi. They have been con- 

 tributory factors in the formation of peat, muck, and brown coal through 

 the centuries, and thev contribute annually to the organic matter of the 

 soil. Thev hold the soil against wind and water erosion, and decrease 

 run-off of water by their spongy texture. They are the food of many 

 small animals. Some species are important pioneers, sharing with the 

 lichens the initial development of soil on bare rocks, volcanic deposits, 

 and newly exposed land. During the World War certain bog mosses of 

 the genus Sphci<imim were collected, sterilized, and used as wound 

 dressings because of their superior absorptixe quality. Peat formed by 

 Spha^^miiih CaUiergon, and other mosses is prized by gardeners as a 

 means of increasing the organic content and porosity of soils in gardens 

 and in lawns. A bale, or about 8 bushels, of peat moss absorbs nearly 

 200 gallons of water. Florists and nurserymen use these mosses as pack- 

 ing around the roots of shrubs and trees when they transport and replant 

 them. 



Approximately 23,000 species of bryophytes have been described and 

 classified. Of these, nearly 9000 are liverworts (Hepaticae), and 14,000 

 are mosses (Musci). 



The moss plant. Some of the mosses and liverworts look much alike, 

 but most of the common mosses are easily recognized. They usually 

 have leafy erect or creeping stems, which develop from a much-branched 

 filamentous or thallose green structure growing on the surface of the soil, 

 and known as the protonema (Gr. first thread). A clone of numerous 

 upright leafv stems mav grow from each protonema. A leafless stalk ma}' 

 eventually develop from the apex or from the side of the leafy stem, 



