CULTURE - SOLUTIONS 



191 



5. Cultivation of Plants in Arti- 

 ficial Soils or Solutions. — The 



soil contains all the chemi- 

 cal elements required by a 

 plant, but the atmospheric air 

 contains only four* elements 

 (N, O, C, H). Those chemi- 

 cal elements present only in 

 the soil are obviously ab- 

 sorbed from that source. But 

 with regard to the four elements 

 present in the soil as well as in 

 the air, experiment alone can 

 decide whence the plant obtains 

 them. In order to decide this 

 question, and to ascertain which 

 elements are absolutely essential 

 to the existence of plants, we 

 cultivate plants with their roots 

 dipping in water containing only 

 certain definite salts dissolved 

 in it (fig. 237); or we may 

 make a simple artificial soil by 

 pouring this nutritive solution on 

 pure insoluble sand. 



A good nutritive solution 

 (termed a "culture solution") 

 can be made up as follows : — 



Fig. 237. — A grass-plant 

 grown with the aid of a 

 culture-solution. 



* Five with Argon. Occasionally, too, the air has impurities such as 

 common salt. 



t The sodic chloride is not absolutely necessary, but serves to keep the 

 plant healthy. 



