COMPOSniON OF I'LANTS. 51 



imioimt of matoriala whioh tho plants cannot take, or do not 

 ni't'd. A fortilo soil is cuimhlo (f rotaining plant food, while 

 sandy soils, owing to tiieir oxoollcni natnral drainago, aro not 

 ft'i'tilo nnli'ss fn-quontly supplicil with manure. 



Two dilTLTciit kinds of plants growijig in the sanio ii'. Id will 

 usually bo found to contain ciTtain substancus in diirercnt i)ro- 

 })()rtion. Soino aro essential, others not ; Home in large quantity^ 

 othcn^ in snudl cpnintity, yet. strange as it may seem, by the 

 chemical composition of a plant we cannot always tell what 

 manures will benclit it most. 



€oii<positioil of Plants. — The combustible ])art of plants is 

 nuido up of five chemical elements — carbon, oxygen, hydrogen, 

 nitrogen aiul sulphur; without these no plant is ever produced. 

 The carbon, hydrogen and oxygen form the cellulose, lignose, 

 pectin, starch, sugar, fat and vegetable acids. The same elements 

 united with nitrogen form the amides and alkaloids; and further 

 united with sulphur the still more important albuminoids. 



Tho incombustible ash always contains five elements — potas- 

 sium, magnesium, calcium, iron and phosphorus, besides sulphur. 

 Iron is present in only very small quantity, liesides these, an 

 ash will generally contain sodium, silicon and chlorine, some- 

 times manganese, and perhaps minute quantities of other elements. 



The earlier chemists spoke of the combustible portions of 

 plants as "organic," and the incombustible portions as "inor- 

 ganic." This distinction is no longer considered accurate. 



Excepting oxygen, these elements are taken from compounds, 

 such as water, carbon dioxide and the substances combined as 

 shown in the following : 



Nitrates. '\ f Ammonia. 



Sulphates. | Potash. 



Carbonates. «--..--..0F--.--> J Lime. 



Phosphates. * " 1 Iron. 



Silicates. Soda. 



Chlorides. J I Magnesia. 



