242 APPLIED BIOLOGY 



posed and barren hillsides, in bogs, in cold northern regions, 

 in forests, and even in water. 



One of the most important is the bog- or peat-moss 

 (Sphagnum) which grows luxuriantly where most other plants 

 cannot live, and its growth gradually fills the bogs with dead 

 vegetation called peat. This does not decay rapidly because 

 the water in peat-bogs is somewhat antiseptic (i.e., prevents 

 the development of bacteria which cause decay elsewhere). 

 In Ireland and some other countries the peat which is ex- 

 tensively used as fuel is composed largely of species of peat- 

 moss or sphagnum-moss. The American peat contains many 

 other aquatic plants. The floating islands in some lakes 

 and the quaking soil in marshy regions are masses of dead 

 vegetation, often largely peat-moss, which have collected 

 some silt and thus formed soil on which other kinds of plants 

 grow. Sphagnum moss is extensively used for packing 

 plants for shipping; and in greenhouses for filling hanging 

 baskets for ferns and orchids, for mixing with soil to prevent 

 it from packing and to make it hold water, and for covering 

 the soil in flower-pots. 



231. Structure of a Moss. Specimens of several common 

 mosses should be collected for comparison in connection with 

 the following account made brief by limitation of the time 

 which can be allowed for study of mosses in a year's course of 

 biology. Specimens of common large mosses should be 

 collected in summer and preserved in formalin-solution. 



Most of our common mosses have erect stems with leaves 

 arranged radially. Sometimes the older part of the stem 

 is prostrate. A section shows no wood-tubes, as in higher 

 plants (ferns and seed-plants), but only a central axis of cells 

 which serve to conduct fluids. At the base of the stem are 

 rootlets or rhizoids, often twisted together. The leaves have 

 a very simple mid-vein of elongated cells, but no such com- 

 plex veining as in higher plants. Some mosses growing in dry 

 places (e.g., Polytrichum) have one side of the leaves specially 



