56 DEPARTMENT OF AGRICULTURE GEORGIA. [342] 



The volatile part, which constitutes on an average about 

 95 per cent, of the whole plant, is composed of carbon, 

 oxygen, hydrogen and nitrogen, with very small quanti- 

 ties of sulphur and phosphorus. They are called volatile 

 elements because they are driven off and mingled with the 

 atmosphere when the organism is burned in the open air. 



The ash elements which remain after the burning as 

 solids, are chiefly phosphorus, sulphur, silicon, chlorine, 

 potassium, sodium, calcium, magnesium, iron and manga- 

 nese, and also small quantities of oxygen, carbon and 

 nitrogen. A few other elements are found in very small 

 quantities too small to require notice here. The elements 

 are given in the above enumeration, but they are usually 

 taken into the organism, and appear in the ash as com- 

 pounds. 



These elements, and their principal compounds of any 

 importance in connection with agriculture, have already 

 been described. 



These various substances, volatile and fixed, enter into the 

 same plant ia a uniform ratio to each other, but in very differ- 

 ent percentages. The importance of any constituent, how- 

 ever, bears no relation to the per cent, in which it is found in 

 the plant. In one sense they are all of equal importance, 

 since the plant cannot attain to full development without 

 the presence of all of these elements, which naturally enter 

 into its composition, in the necessary ratio to each other. 



Though the ash elements occur in relatively very small 

 quantity, they are essential to the perfect development of 

 the plant, and are, together with nitrogen, the first which 

 need to be artificially supplied to the soil. The atmos- 

 phere affords an inexhaustible source of the prominent 

 volatile elements of plant food. 



Wolff and Knop give the following percentage from all 

 the trustworthy analyses made of agricultural plants all 

 of them air-dried, except the last : 



