[Chap. I PLANT SCIENCE 3 



the life histories of plants; or by a study of plants in relation to soil and 

 climatic conditions. Other problems have been solved through the dis- 

 covery of facts about the growth of bacteria and fungi, their various 

 effects on the growth of other organisms, and the means of controlling 

 their development. 



Numerous unsoKed problems remain. That societv recognizes the 

 need of continued and far-reaching research with plants is attested by 

 its maintenance of forest and agricultural research stations in every 

 country and in nearly every state and province throughout the world. 

 Through the years these institutions have provided an increasinglv im- 

 portant addition to research by teachers and graduate students in col- 

 leges and universities. As a result of these investigations each generation 

 has an increased wealth of botanical knowledge available for both per- 

 sonal and social needs. Through instruction one may readilv learn how 

 to select and apply a portion of this accumulated knowledge. 



Thus far we have stressed the importance of plants and of the science 

 of plants mainly in relation to human economics, occupations, health, 

 and the survival of all animals. The general desire of man to know and 

 interpret his environment and to speculate about himself and his environ- 

 ment must also be emphasized here. Plants are a conspicuous and impor- 

 tant part of that environment. In addition to the interrelations of plants 

 and animals there are many important relations among plants them- 

 selves, between plants and their phvsical environments, and between 

 the parts of each individual plant. These interrelations have been and 

 still are interpreted on the basis of several diverse assumptions ranging 

 from magic to science. Throughout the ages some of these interpreta- 

 tions, whether obtained in the classroom or elsewhere, whether correct 

 or incorrect, have become a part of the general outlook and culture of 

 everyone. A study of plants as part of a general education would be 

 quite inadequate unless it included interpretations of these interrelations 

 based on present scientific knowledge and method. In the chapters that 

 follow we shall find that an understanding of these interrelations on the 

 basis of evidence is not only a matter of personal interest, but one that 

 is both desirable and necessary for the welfare of society. 



What is a plant? When we pull weeds in a garden, mow the grass on 

 a lawn, enjoy the shrubs and trees in parks and forests, we readily recog- 

 nize these living organisms as plants. Stale bread and fruit may be cov- 

 ered with mold ( Fig. 1 ) . We have all seen otlier fimgi ( Fig. 2 ) in the 

 form of mushrooms in fields and woods. The surfaces of ponds and moist 



