I.] ELEMENTS PRESENT IN PLANTS 3 



phosphorus, sulphur, and to a smaller degree, chlorine. 

 Similarly we shall always find five metallic compounds, 

 — potash, soda, lime (oxide of calcium), magnesia, and a 

 smaller quantity of iron ; when we are dealing with 

 cereals or grasses, there will also be a large proportion 

 of silica in the ash, though it is absent or only found in 

 very small quantities in the ash of other plants. Thus 

 we distinguish in the plant, (i) water; (2) a combustible 

 part, of which carbon is the base ; and (3) a small pro- 

 portion of incombustible mineral ash. There remains 

 another element which disappeared with the combustible 

 portion, but which belongs neither to the carbon nor to 

 the hydrogen and oxygen with which the carbon are 

 mainly combined. To detect it we must mix some of 

 the dry plant material in a test-tube with lime, or 

 better with the mixture called soda-lime, and then 

 heat the whole ; gases will soon be given off in which 

 we can detect the familiar smell of ammonia or hartshorn. 

 Now ammonia is a compound of the element nitrogen, 

 and ammonia is as a rule liberated from any compound 

 of nitrogen with carbon and its associated elements, 

 hydrogen and oxygen, when the compound is heated 

 with lime or other alkali. A proper analysis will 

 show that only i to 2 per cent, of the dry matter of 

 the plant consists of nitrogen, but it is an indispensable 

 element and always found in the plant. 



To illustrate more definitely what may be expected 

 in the plant and in what proportions, in Table I. is set 

 out a list of the quantities of the various elements found 

 in the grass cut from an average acre of land at the 

 time it was ready for mowing, this example being 

 chosen because it gives a composite analysis represent- 

 ing a large variety of plants. The analys"s is set out 

 both in pounds per acre, and as percentages of the 

 whole plant and of the dry matter respectively. 



