CHAPTER X. 



THE NUTRITION OF PLANTS. 



110. Physiology. — In the previous chapters plants have 

 been considered in reference to their surroundings. It 

 was observed that various organs of nutrition hold certain 

 life-relations, but it is essential to discover what these rela- 

 tions mean to the life of the plant. The study of plants 

 from the standpoint of their life-relations has been called 

 Ecology ; the study of the. life-processes of plants is called 

 Physiology. These two points of view may be illustrated 

 by comparing them to two points of view for the study of 

 man. Man may be studied in reference to his relation to 

 his fellow-men and to the character of the country in which 

 he lives ; or his bodily processes may be studied, such as 

 digestion, circulation, respiration, etc. The former cor- 

 responds to Ecology, the latter is Physiology. 



All of the ecological relations that have been mentioned 

 find their meaning in the physiology of the plant, for life- 

 relations have in view life-processes. The subject of plant 

 physiology is a very complex one, and it would be impossi- 

 ble in an elementary work to present more than a few very 

 general facts. Certain facts in reference to plant move- 

 ments, an important physiological subject, have been men- 

 tioned in connection with life-relations, but it seems neces- 

 sary to make some special mention of nutrition. 



111. Significance of chlorophyll — Probably the most im- 

 portant fact to observe in reference to the nutrition of 

 plants is that some plants are green or have green parts, 

 while others, such as toadstools, do not show this green 



