WATER CONTENT AND ASH OF PLANTS 163 



and also oxygen, which is in chemical combination with 

 all of the above elements. 



The essential ash elements are absolutely necessary 

 for the normal growth and development of plants. They 

 take a direct part in the production of plant tissue. The 

 part which each ash element takes in plant growth 

 has been known only for a comparatively short time. At 

 one time, it was believed that the ash elements were 

 largely accidental that the plants in taking up water from 

 the soil could not well keep out the soluble earthy mat- 

 ters, but the methods of sand and water culture have 

 demonstrated the necessity and the functions of the 

 various ash elements. 



211. Water Culture. In water-culture experiments, 

 the seed is germinated and then the roots 

 are suspended in water containing small 

 amounts of the different ash elements. The 

 roots are protected from the light, and the 

 solution is frequently changed. In case it 

 is desired to learn what effect the absence 

 of an element has upon the growth and de- 

 velopment of the plant, all of the elements 

 are supplied in known amounts except the 

 one in question which is withheld alto- 

 gether. The development of the plant is 

 observed, and if it reaches maturity and 

 produces fertile seeds, it is concluded that 



Fig. 69. Water 



the element withheld is not necessary to plant culture, 

 growth, while on the other hand, if the plant does not de- 

 velop naturally, the element withheld is considered a nee- 



