2 General Botany 



petroleum, and natural gas, although obtained from the earth, 

 are the products of plants which lived in former geological times. 

 When wood is burned, the great store of energy which the tree has 

 accumulated from sunlight is released in the form of heat. When 

 coal, petroleum, or natural gas is burned, the energy stored by 

 plants from sunlight of former geological ages is liberated. 



3. Plant fibers. Of almost equal importance is the production 

 of fibers for clothing and many other articles. Such plants as 

 cotton, flax, and hemp supply the bulk of these fibers, and the 

 fibers not directly derived from plants come from animals that 

 feed on plants. Artificial silk and vegetable wool are recent 

 substitutes for animal fibers that are being manufactured from 

 plant fibers. \ 



4. Wood products. Lumber is a primary necessity in the con- 

 struction of houses and buildings of all kinds. It is also the chief 

 material for furniture and countless other articles of household 

 use and ornament. Paper, the principal medium of communica- 

 tion and commercial exchange, is also essentially a wood product. 



5. Oils, resins, and drugs. Plants have played an important 

 part in the progress of civilization by supplying oils and fats, 

 gums, resins, dyes, rubber, drugs, alcohols, cork, the materials for 

 explosives, and many other basic substances for the arts and in- 

 dustries. 



6. Other uses of vegetation. Trees and grasses are the great 

 stabilizers of the soil on mountains and in valleys. They help to 

 retain flood water and prevent destructive erosion. They pro- 

 vide food and shelter for numerous wild animals that are of great 

 economic importance. The plants of our lakes, ponds, and 

 streams are the primary sources of food and shelter for fishes, 

 ducks, and other water animals. 



7. Importance of bacteria and fungi. Certain small plants, the 

 bacteria and fungi, are beneficial in bringing about the decay of 

 the bodies of plants and animals. This results in the production 

 of substances that can be used again by green plants in the mak- 



