CHAPTER IV 

 PLANT PHYSIOLOGY 



102. Plant Physiology has for its subject the study 

 of the activities of the plant and of its parts. It is not 

 sufficient to learn about the morphology, i.e. the external 

 and internal structure; we must also seek to learn what 

 the different parts are for, how the plant carries on its 

 activities and the relations of the plant to the external 

 surroundings. In the preceding chapters the functions 

 of the parts have been mentioned briefly in connection 

 with the special structures. In this chapter, it is sought 

 to take up the plant activities as a whole. Much of 

 what is here given can be used by the skillful teacher at 

 the same time that the foregoing chapters are being 

 studied. 



Plant Physiology will be treated under the following 

 heads: (1) Nutrition, (2) Growth and Reproduction, 

 (3) Movements. To these will be added (4) a short 

 consideration of the Pathology of Plants. 



103. Nutrition, in its widest sense, includes the taking 

 in and giving out of water and other substances, their 

 transportation from one part to another in the plant, 

 their use in the plant in the formation of food, the use 

 of this food, and the energies required or set free in all 

 these processes. 



104. The most important single substance taken in 

 by a plant is, beyond doubt, water. The driest plant 

 parts, such as seeds, possess from 5 to 10 per cent, or 

 more of water while leaves may possess 75 per cent, or 



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