202 COLLEGE BOTANY 



and may also be an important element in the nucleoproteins. 

 Under some conditions it is injurious to plant growth. 



(d) Calcium is an important element in the metabolism of 

 the plant. The use of lime on soils is very generally practiced 

 in the growing of many crops. It is supposed to be an important 

 factor in the functions of chlorophyll and there is some evidence 

 of the definite relationship between the calcium in the plant and 

 starch digestion. It has been demonstrated that the presence of 

 calcium in the soil tends to counteract the toxic action of mag- 

 nesium. It is also well known that if used in sufficient quantity 

 it will overcome the acidity of the soil and make conditions more 

 favorable for the growth of many plants. 



(e) Iron, in very small quantities, appears to be necessary 

 for plant growth, but its exact functions are not well understood. 

 It is necessary for the formation of chlorophyll, and it is prob- 

 ably used in very small amounts by every living cell of the plant. 

 When it is withheld, growing plants soon become pale or chlor- 

 otic and weak. 



(/) Sodium is not required by plants, but may, under cer- 

 tain conditions prove beneficial. It may be advantageous to grow- 

 ing plants by making other salts available, especially potassium. 



(g] Chlorine is not generally considered essential for plant 

 growth, but may be important in some cases. 



(h) Sulfur is very important and is essential in albuminous 

 compounds. However, it is used in extremely small quantities. 



(t) Silicon is very generally found in many plants, but does 

 not appeal' to be necessary for their growth. It is utilized in 

 many plants, such as horsetails or Equisetums, for mechanical 

 strengthening of the cell walls. 



Chemical Analysis of Plants and Soil. From a study of the 

 preceding, it will be readily seen that a chemical analysis of the 



