2 TEXTBOOK OF BOTANY 



nished. Much of our clothing is made from plant fibers. Paper and rubber 

 made from plant products have increased our means of communication 

 and transportation. Many of our beverages and some of our important 

 medicines contain plant derivatives. A large part of the population earns 

 a living by supplying itself and the rest of society with plant parts or 

 plant products. 



Certain of the larger plants are used to beautify our homes, to decorate 

 the landscape, and in other ways to add to the enjoyment of living. We 

 use trees to protect us from intense heat and light. Forested areas have 

 become the centers of many forms of sport and recreation. They are also 

 continuous sources of cover and food to countless animals both large and 

 small. Plants not only hold the soil against erosion by wind and water, 

 but they improve its texture and composition; and myriad microscopic 

 plants contribute to its fertility. 



But the relation of plants to animals is not wholly beneficent. Weeds, 

 for example, may decrease the yield of crops and increase the labor of 

 cultivating them. Many plants contain toxic and irritating substances that 

 cause suflFering, illness, or the death of human beings and other animals. 

 Certain microscopic plants may invade the tissues of the animal body 

 and lead to disease and death. Others cause diseases and destruction of 

 the larger plants, and still others grow on commercial food products in 

 shipment and storage and lessen their value or destroy them. Such plants 

 test the ingenuity of every generation of human beings to devise means 

 of avoiding, controlling, or eradicating them. 



The value of plant science to society has been increasingly appreciated 

 as knowledge of plants has advanced. The farmer who plants a field; the 

 orchardist who attempts to secure a crop of fruits; the florist who seeks 

 the production of ornamental plants and flowers; the forester who tries 

 to obtain a profitable yield of timber on a tract of land; the gardener who 

 supplies our markets with edible and succulent leaves, stems, and roots; 

 industriahsts who seek to find new sources and new forms of plant prod- 

 ucts to meet our social needs; and the conservationists who strive to 

 preserve our soils from wind and water erosion and to rescue our disap- 

 pearing fish and game animals — all these find themselves confronted by 

 an often bewildering array of problems that lie within the field of plant 

 science, or botany. 



Many of these problems have been solved by a study of the structures, 

 the chemical composition, the physiological processes, the heredity, and 



