Economic Importance of Plants 257 



of their oil content, are used in the manufacture of burning flashlights 

 as well as certain kinds of dusting powders. The spores of certain club 

 "mosses" or "ground pines" are very inflammable, for which reason they 

 are used in fireworks under the name of vegetable sulfur. Certain types of 

 coal were deposited in past ages through the carbonized remains of cer- 

 tain treelike club "mosses," scouring rushes, and primitive seed plants. In 

 general, the ferns and their allies are of small economic importance to- 

 day, although at one time they dominated the vegetation of the earth. 



V. ECONOMIC IMPORTANCE OF GYMNOSPERMS 



(Figs. 52 to 54) 



The cone-bearing trees, known as conifers, are ranked high in the 

 production of valuable timber, as is verified by the use of yellow pines, 

 redwoods, pitch pines, firs, cedars, hemlocks, and white pines. In 1930 

 over 7,500,000,000 board feet of yellow pine alone were cut in the 

 United States. Pine lumber is one of the most valuable and widely used 

 kinds because it is durable due to its composition, it is easily worked, 

 and it is quite resistant to the attacks of insects, probably because of its 

 resin content. Certain conifers are used extensively in the manufacture 

 of wood pulp. Red cedars are used in making pencils, cigar boxes, 

 chests, trunks, and posts. Conifers yield large quantities of resins, oils, 

 and amber products used in arts, industries, and medicine. Examples 

 are turpentine, balsam, spruce gum (for chewing gum), oil of juniper, 

 and oil of savin. Certain species of pine provide edible seeds used by 

 human beings for foods. The edible or nut pine of western United 

 States and the sugar pine of California are examples. The barks of such 

 conifers as hemlock and spruce furnish important materials for use in 

 the tanning of skins of animals for leather. Thousands of youngsters, 

 and probably as many adults, are made happy at Christmas time by the 

 decorated conifers. This use of conifers for this purpose has become so 

 extensive that the cultivation of desirable types has become necessary in 

 order to supply the ever-increasing demands. The wood of spruce trees 

 is particularly resonant so that it is used in making certain types of 

 musical instruments. The remains of conifers are often found as fossils 

 and as fossil-resin amber in which other fossils may have been imbedded. 



VI. INDUSTRIAL PLANTS 



Industrial plants may be considered as those which yield materials 

 used in such industries and arts as spinning, weaving, dyeing, painting, 

 paper making, building, tanning, sculpture, carving, manufacture of 

 foods, medicines, etc. 



