CHAPTER XVIII 



ABSORPTION OF WATER AND INORGANIC SALTS 



Plants take in and give out water. — If flowering plants be 

 not supplied with water, they not only cease growing, but they 

 droop, wither, and finally die. This familiar fact demonstrates 

 that the plants both absorb and give off water. 



The roots are the water-absorbing organs. — If we supply 

 water to the leaves and stems of an ordinary flowering-plant, 

 but keep the soil dry, the plants 

 wither. This proves that the 

 shoot is not able to absorb suf- 

 fiicient water. It is easy to show 

 that roots absorb water ; we 

 merely have to watch the diminu- 

 tion of the water from culture- 

 solutions in which the roots are 

 growing. By the aid of the 

 simple apparatus given in fig. 

 241 it is possible to measure 

 exactly the rate at which the 

 roots are sucking water in. 



The roots also absorb salts 

 dissolved in water. — This state- 

 ment is easily proved by observ- 

 ing that the salts in culture- 

 solutions decrease in amount as 

 the roots absorb water. 



Salts can be taken in by a root only when they are dis- 

 solved in water. — It is not easy to prove this statement without 

 the use of the compound microscope; but three experiments 

 illustrate the truth. If, instead of growing seedlings with the 

 help of a culture-solution, we give them water to which have 

 been added insoluble salts of all the chemical elements required 



203 



Fig. 241. — A thin, bent glass-tube 

 filled with water, and a plant, are 

 fixed, as figured, by means of an air- 

 tight cork, into a bottle full of water. 

 As the root absorbs, the rate at which 

 the water is sucked along the tube is 

 noted by the aid of a graduated piece 

 of cardboard. 



