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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