182 Plant Physiology 



Knop and other students of nutrition so regarded it, and 

 it is sometimes omitted from the nutrient solution. It is 

 an invariable constituent of the soil solution, and either 

 on this account, or in the belief that it is generally some- 

 what advantageous, it is commonly added to the nutrient 

 ration as NaCl or KC1. 



Nobbe and others have found KC1 indispensable in the 

 proper maturity of buckwheat, which, deprived of it, 

 develops a pathological condition at or following the period 

 of flowering, resulting in a failure to form seed. A light 

 fertilization of special crops with sodium chlorid has not 

 infrequently resulted in increased yield ; but in most cases 

 it is not certain that the action is direct, and even less clear 

 that it is the additional chlorine which is important in the 

 substance employed. This relation of plants to chlorine 

 is the second notable difference in the metabolism of 

 plants and animals. 



99. Sulfur. Sulfur is primarily important because of 

 the fact that it is contained in albuminoidal compounds. 

 It occurs in some of the by-products of protein production, 

 and also as sulfates of the bases especially potassium 



occurring in the cell-sap. It is usually required in such 

 limited quantity that the seed may furnish all that is 

 needed for the normal growth of the plant through a con- 

 siderable period. 



100. Silicon. Silicon forms a predominant part of the 

 ash of many grasses and other plants. It accumulates in 

 old stems and caulms, and may constitute from 40 to 

 70 per cent of the ash of cereal straws and corn stover. 

 Nevertheless, corn may be grown without any further 

 addition than that furnished by the seed. One of the 



