v] NATURE OF PLANT-ANIMALS 141 



and thus to augment its living substance, integral 

 parts of which consist of organic, nitrogen-containing 

 compounds. That such plants suffer not infrequently 

 from nitrogen-hunger is one of the most important 

 agricultural discoveries of the last century. As a 

 consequence of the recognition of this fact, many 

 thousands of tons of nitrate of soda from the nitrate 

 beds of S. America and equally vast quantities of 

 sulphate of ammonia a bye-product of the distil- 

 lation of coal are added annually by the farmer to 

 his land. Nor is the origin of this nitrogen-deficit 

 far to seek. The nitrogen contained in the nitrates 

 of the soil comes in the plant to form a constituent 

 of the organic nitrogen compounds, such as the pro- 

 teins. The plant dies and decays, or is eaten and 

 the eater decays. Ultimately, as the result of these 

 processes of decay, water and carbon-dioxide are 

 liberated and may at once be brought again, by the 

 agency of the green plant, into the vital circulation. 

 Synthesised to form carbohydrates, these substances 

 are once more available for the nutrition of plants 

 and animals. But with respect to nitrogen it is 

 otherwise. The organic nitrogen compounds of the 

 dead animal or plant are broken down by the bacterial 

 and fungous agents of decay into a series of simpler 

 forms which, acted on by yet other of the ordered 

 army of saprophytic micro-organisms, yield finally 

 ammonia and nitrogen. The nitrogen leaks away 

 into the atmosphere and contributes to the 79 per 



