CHAPTER X. 



THE CONSTITUENTS OF PLANTS. 



I. THE WATER IN THE PLANT. 



214. Amount of Water in Plants. All living parts of 

 plants are abundantly supplied with water. It is always 

 present in living protoplasm, and the greater its activity the 

 more watery is its composition. The cell-walls of living 

 tissues also contain large quantities of water ; and in plants 

 composed of many cells (as the larger flowering plants) even 

 those cells and tissues which have lost their activity generally 

 have their walls saturated with water. In ordinary herbace- 

 ous land plants the amount of water is not far from 75 per 

 cent of their whole weight ; thus in growing rye it is about 

 73 per cent ; in meadow grass, before bjossoming, 75 after 

 blossoming, 69 ; in lucerne, when young, 81 in blossom, 74 ; 

 in white clover, 80 ; in red clover, before blossoming, 83 

 after blossoming, 78 ; in oats, in blossom, 81 ; in Indian 

 corn, in blossom, 84. In certain parts of plants the per- 

 centage is still higher ; for example, in the leaves of the field 

 beet it is 90 ; in tubers of the potato, 75 ; in the thickened 

 root of the parsnip, 88 ; in the similar root of the turnip, 

 92. In aquatic plants the percentage is much higher, often 

 exceeding 95 ; it is so abundant in many of the simpler 

 forma that upon drying nothing but an exceedingly thin and 

 delicate film is left. 



215. Water in the Protoplasm. As explained in para- 

 graphs 4 and 5 (page 5), living protoplasm has the power 

 of imbibing water, and thereby of increasing its fluidity. 

 Even after it has imbibed all the water which it can retain 

 it continues the process, and separates the surplus in drops 



