256 Plant Biology 



stated that certain specific kinds of bacteria are necessary for the desirable 

 decomposition of waste materials in the human large intestine. Naturally, 

 not all types would be desirable for this important work. If the bac- 

 terial flora of the large intestine is not normal, there may result a variety 

 of abnormal conditions. 



III. ECONOMIC IMPORTANCE OF BRYOPHYTES 



(Figs. 43 to 46) 



Peat mass (Sphagnum) (Fig. 46) is used for packing materials in ship- 

 ping, in surgical dressings, in gardening, and similar ways. In gardening 

 the peat moss retains soil moisture and prevents weed growth. One 

 species of sphagnum can absorb approximately twenty times its weight of 

 water. Certain kinds of coal were formed by an accumulation of the re- 

 mains of sphagnum mosses in swamps and open waters of past ages. Peat 

 is formed by sphagnum moss and, when dried, is used as fuel in certain 

 communities where other materials are not available. A few species of 

 bryophytes are the sources of certain chemicals and medicines. Undoubt- 

 edly certain bryophytes are of some importance in the destruction of 

 rock into soil. They may also aid in preventing soil waste by erosion. 

 As compared with other phyla of plants, bryophytes are of small eco- 

 nomic importance to man. 



IV. ECONOMIC IMPORTANCE OF FERNS AND 

 THEIR ALLIES (Figs. 50 and 51) 



The larger roots of certain species of ferns contain considerable 

 starch and are consequently used as food. Certain species of ferns con- 

 tain a substance known as coumarin which is used in making certain 

 perfumes. Other ferns contain such chemicals as tannin, aconitic acid, 

 or ethereal oils which may be used for commercial purposes. Ferns 

 have been used in the preparation of certain medicines. Certain varie- 

 ties of ferns produce stock poisoning when eaten by domestic animals. 

 The horsetails or scouring rushes (Equisetum sp.) (Fig. 49) may be 

 used for scouring or polishing purposes. The growing of these plants 

 along certain slopes of land may prevent soil erosion. The presence of 

 horsetails along the edges of swamps may help in the transformation of 

 the swamp into a marshlike area by retaining soil particles around them. 

 They add to the land area in this manner at the expense of the water 

 area. 



Certain tropical club "mosses" are used for medicinal purposes. The 

 spores of certain club "mosses" (Lycopodium clavatum) (Fig. 47) because 



