CHAPTER V. 



THE CHEMISTRY AND PHYSICS OF PLANTS. 



124. The Water in the Plant. — All living partB 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 tis- 

 sues 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 ordi- 

 nary herhaceous land-plants the amount of water is not far 

 from 75 per cent of their whole weight. In aquatic plants 

 the percentage is much higher, often exceeding 95 ; it is 

 so abundant in many of the simpler forms that upon dry- 

 ing nothing but an exceedingly thin and delicate film is 

 left. 



125. Water in the Protoplasm. — As explained in para- 

 graph 4 (page 2), living protoplasm has the power of im- 

 bibing 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 in 

 its interior — the so-called vacuoles. Now an examination 

 of the cells of rapidly growing tissues shows that their 

 protoplasm is much more watery than that of living but 

 dormant tissues — e.g., those of seeds — and one of the first 

 signs of activity in the latter is the imbibition of water. 



