ESSENTIALS OF PLANT LIFE 2Q 



Lime : Magnesia : : i : I for oats, 

 : : 2 : i for barley, 

 1:3:1 for wheat. 



Lime, 1 he says, is required for foliage, and magnesia for seed; 

 the greater the proportion of foliage to seed, the greater the ratio 

 of lime to magnesia required by the plant. 



Several factors operate to prevent injury by an unfavorable 

 ratio of plant food in the soil. The root of the plant exercises a 

 certain degree of selection by which it may to some extent de- 

 cline to absorb undesirable plant food. In some plants an excess 

 of lime is deposited in cells in the form of calcium oxalate, in 

 others, it forms a white coating (probably carbonate of lime) 

 upon the leaves. There is a difference of opinion as to the 

 significance of Loew's work. According to Hopkins' experi- 

 ments, 2 the quantity of lime and magnesia are of more importance 

 than the ratio. 



The importance of the ratio of lime to magnesia in practical 

 farming remains to be decided by field experiments. 



Plant Stimulants. Substances which exert an appreciably 

 favorable action upon plant growth and at the same time are not 

 essential to the life of the plant, may be termed stimulating com- 

 pounds. According to Loew 3 and his pupils, borax and salts of 

 lithium, caesium, uranium, manganese, bromine, iodine, fluorine, 

 and ferrous iron act as plant stimulants in small doses ; in large 

 quantities, they may prove injurious. The more important 

 of these stimulants 4 appear to be manganese, iron, and 

 fluorine. It is also possible that certain organic substances 

 may act as stimulants in small doses, or as poisons in large 

 doses. According to Loew, the favorable quantity of the stimu- 

 lants named is as follows : Manganous sulphate about 75 pounds 



1 See also Circ. No. 10, Porto Rico Exp. Sta. : Bui. 45, Bureau of Plant 

 Industry. 



2 Soil Fertility and Permanent Agriculture, p. 170. 



3 Bui. Tokyo Univ., 1904, p. 163. 



4 Int. Cong. App. Chem., 1912, 15, p. 39. 



