434 BIOLOGY AND HUMAN LIFE 



used in emergencies as a dressing for wounds ; large quantities 

 were used in this way during the World War. When dry it 

 makes a useful packing material, but is now used almost en- 

 tirely for packing plants. Generally speaking, however, the 

 mosses are of little direct use to us, although they are very 

 interesting plants and probably play a part in the gradual con- 

 version of the soil into a place suitable for higher plants. 



The ferns in past ages reached gigantic size and probably 

 furnished most of the fuel that we use today as coal. Aside 

 from those gathered and cultivated for ornamental purposes the 

 horsetails have been used for scouring, as the cells contain a 

 considerable amount of hard silica, the same substance as sand. 

 The club mosses, or "Christmas moss," were formerly of value 

 because they furnished the lycopodium powder which may still 

 be obtained in the drug stores. This powder consists of masses 

 of spores (see page 470) which on account of an oily substance 

 cannot get wet, and was therefore used as a coating for pills, to 

 keep them from sticking together, and for many purposes that 

 are now served by the mineral talcum powder. 



322. Gymnosperms (naked-seed plants). The cone-bearing 

 trees represent a family that is of great importance both for the 

 timber that it furnishes and for the value of the standing forests. 

 All our soft woods except the whitewood (tulip tree) and poplar 

 come from this group — the pines, cedars, spruces, firs, redwoods, 

 etc. The maidenhair tree, the ginkgo, has been introduced from 

 Japan as an ornamental tree. The cycad, resembling the palms 

 in some ways, links this group with extinct forms related to the 

 giant ferns. Many of them are represented in the coal deposits 

 in various parts of the world. The conifers furnish, besides tim- 

 ber, large quantities of resin and turpentine, and pulp for paper. 



323. Monocotyledons. More than 25,000 distinct species of 

 plants belong in this division, classified in some forty families. 

 Half a dozen of these families are of marked importance to 

 mankind, although each of the others may be related to our 

 affairs in one way or another. While we shall note only the out- 

 standing values or injuries that make members of each family 



