80 DEPARTMENT OF AGRICULTURE GEORGIA. [366] 



ate ; sulphate of lime has the opposite effect of fixing the 

 ammonia in an available form the sulphate and hence 

 its incorporation with animal manures is very desirable. 



From forty to fifty per cent, of pure, high-grade super- 

 phosphate is sulphate of lime, or gypsum, and hence the 

 application of gypsum to composts, in which superphos- 

 phate is used, is not necessary. 



The beneficial effect of sulphate of lime, when applied 

 as a top-dressing to plants, especially to legumes, is at- 

 tributed to its power of fixing ammonia from the air. 



THE ATMOSPHERE IN ITS RELATIONS TO VEGETATION. 



There is a mutual relation between the atmosphere, 

 plants, and animals, which beautifully illustrates the econi- 

 omy of nature. 



The atmosphere is a mechanical mixture of oxygen and 

 nitrogen, with small quantities of carbonic acid, ammonia, 

 and watery vapor. Its composition is nearly invariable at 

 all points on the surface of the earth, its uniformity being 

 preserved by winds and currents. 



Though the per cent, of carbonic acid in the atmosphere 

 is extremely small, plants derive all of their carbon from 

 it, through the medium of their leaves and other green 

 parts. 



"Every six pounds of carbon in existing plants have 

 withdrawn twenty-two pounds of carbonic acid gas from 

 the atmosphere, and replaced it with sixteen pounds of 

 oxygen gas, occupying the same bulk." GRAY. 



The carbo-hydrates, or heat and fat producing constitu- 

 ents of plants, sometimes called the ternary compounds, 

 from the fact that they are composed of three elements 

 carbon, hydrogen, and oxygen are derived principally 

 from the atmosphere ; though the hydrogen is probably 

 absorbed entirely by the roots, in water, and oxygen in 

 part from the same source. 





