S '".INTRODUCTION 



Plant physiology treats of the plant in action, how it lives, 

 respires, feeds, grows, and produces others like itself. It dis- 

 cusses the nature of the material in which the life activities of 

 the plant have their origin, and the conditions as regards light, 

 heat, air, and moisture under which life is possible. It considers 

 the raw materials out of which plant food is made, the processes 

 by which the manufacture is carried on, and the means by which 

 food once produced is transported throughout the plant body. 

 The mode of growth of plants is an extended and most impor- 

 tant topic, and the processes by which reproduction is carried 

 on are so numerous and complicated that they constitute one 

 of the most difficult and interesting departments of botany. In 

 order to go far into the details of the life activities of plants one 

 needs to know a good deal of chemistry and some physics. But 

 there are many of the phenomena of plant physiology which 

 can be taken up with profit in an elementary way and investi- 

 gated with rather simple apparatus. 



Plant geography discusses the distribution of the various 

 kinds of plants over the earth's surface. 



Paleobotany, usually studied along with geology, considers 

 the history of plant life on the earth from the appearance of 

 the first plants until the present time. 



Taxonomy, or systematic botany, is concerned with the classi- 

 fication of plants. By this is meant the arrangement or grouping 

 of the kinds of plants to show their relationships to one another. 

 It attempts to express the final results of the long processes of 

 plant evolution, and is far more than the conventional study of 

 flowering plants, which occupy only the highest grades in the 

 elaborate system of plant evolution and classification. 



Plant ecology treats of the relations of the plant to the con- 

 ditions under which it lives, together with the origin and devel- 

 opment of plant associations. Under this division of the science 

 are studied the effects of soil, climate, and friendly or hostile 

 animals and plants on the external form, the internal structure, 

 and the habits of plants. The main lesson to be learned from 



