30 



ELEMENTARY BIOLOGY 



From experiments in which the various materials that make 

 up soil (such as sand, clay, and the various salts) are used 

 separately and in combinations, we learn that it is not the 

 sandiness of the soil, or the color, or merely the water in it 

 that makes the growth of plants possible. We find that it is 

 somctJiing in the soil that can dissolve itt zvater. 



48. The salts of the soiL These soluble substances in the 

 soil are the salts, of which there are many different kinds. 

 Are all these salts related to plant growth, or only a certain 

 few — or perhaps only one } These questions have been 

 answered by means of carefully planned and carefully conducted 

 experiments. In these experiments plants were grown in solu- 

 tions of soil minerals from which now one element and now 

 another was omitted. 



It is found that the omission of some elements will absolutely 

 prevent the further growth of the plants, whereas the omission 

 of others will make no perceptible difference. From the results 

 of such experiments the following table has been constructed : 



