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 

 something in the soil that can dissolve in water. 



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 : 



ELEMENT OCCURRENCE IN PLANTS 



SPECIAL FUNCTION 



Aluminum 

 Calcium 



Chlorin 

 Iron 



Magnesium 

 Manganese 

 Phosphorus 



Potassium 



Silicon 

 Sodium 



Sulfur 



In lower parts 



In leaves and stem 



In lower parts 



In leaves and stem 



In seeds and leaves 

 In lower parts 

 In seeds 



In actively growing 



parts 



In stems and leaves 

 In stems and roots 



In all growing parts 



No function. 



Related to the formation of plant cells ; 



" makes plants hardy." 

 No function, so far as known, although 



present universally. 

 Related to the formation of chlorophyl 



(see p. 54). 



Related to the formation of seeds. 

 No function. 

 Related to the activities of leaves ; takes 



part in the formation of proteins (see 



p. 56). 

 Related to the formation of starch and 



sugar, and to the growing process. 

 No special function. 

 No function, although present almost 



universally. 

 Necessary to the formation of proteins. 



