Manures and Manuring 141 



Before we consider the application of manures to the soil it is necessary 

 to refer again to van Helmont's experiment with the Willow, already 

 described at p. 108. That experiment clearly proved that the great bulk 

 of a plant's weight came, not from the soil, but from the air and from 

 water. Carbonic acid gas (of which there are only 4 volumes out of 10,000 

 in the atmosphere) supplies all the carbon that is necessary, so long as 

 the cultivator is sensible enough to allow his plants sufficient space and 

 light, and does not overcrowd them. This carbon, which makes up the 

 great bulk of the dry weight of every plant, is obtained absolutely free 

 of charge from the air, and there is not the slightest danger of the supply 

 becoming exhausted. The carbon from the air and the water from the 

 soil make up from 95 to 99 per cent of the weight of all plants, thus 

 leaving from 1 to 5 per cent of material to be provided by the soil alone. 

 Perhaps this fact will be made more clear by the following analysis of 

 the wheat plant, taken from Sowerby's Thorough Cultivation: 



COMPOSITION OF WHEAT PLANT 



Per Cent. 



Carbon 47 -69 "j 93 -55 per cent of the whole 



Hydrogen ... ... ... 5 '54 j- = plant obtained from the air 



Oxygen ... ... ... 40'32 J and water. 



Soda 0-0 



Magnesia . . . 

 Sulphuric acid 

 Chlorine 

 Oxide of iron 

 Silica 



3 '386 per cent of foods, which 

 as a rule are present in large 

 quantities in the soil (see 

 p. 110), and have to be rarely 

 applied artificially. 



Manganese 0'2S 



3 '00 per cent of foods which 

 Nitrogen ... ... ... 1'60 "| the soil contains in limited 



Phosphoric acid ... ... 0*45 I quantities (see p. 110), and 



Potash ... ... ... 0'66 j which must be rendered 



Lime ... ... .;. 0'29 J available by cultivation or 



supplied by manures. 



From this table it becomes evident that the art of manuring the soil 

 is narrowed down in a very remarkable degree. As with wheat, so with 

 other crops. The cultivator has not to concern himself with providing 

 oxygen, carbon, or hydrogen so long as he allows his plants plenty of 

 fresh air and a proper supply of moisture. He is actually relieved of the 

 burden of finding over 93 per cent of the material which makes up his 

 crops. The other 3*386 per cent, consisting of soda, magnesia, sulphuric 

 acid, chlorine, oxide of iron, silica, and manganese, he also very rarely has 

 to trouble himself about, as they are generally present in great quantities 

 in the soil. But he must remember that those inorganic foods can only 

 be liberated and brought into an available form by the constant use of 

 the spade, the fork, the plough, the hoe, &c.; in fact, by cultivation or 



