26 



GARDENING FOR THE SOUTH. 



Hal to the growth of plants. What are these substances I 

 If yon burn dried vegetables, a few ashes only remain ; 

 less than one-tenth of their substance. This is all the plant 

 got necessarily from the soil. Over ninety per cent, has 

 escaped into the air, from which the plant derived it 'imme- 

 diately or remotely. The composition of their ashes, va- 

 ries in different species of plants, and slightly in the same 

 species, when grown in different soils ; but they are always 

 a valuable manure for that species, and when slowly dis- 

 solved in the soil, furnish the roots with just the salts re- 

 quired to nourish the growing plant. 



But over nine pounds in every ten, have disappeared 

 under the action of fire. The substances expelled are car- 

 bon, hydrogen, oxygen and nitrogen ; all essential to 

 growth, and which must be furnished to the plant, or it 

 will perish. Carbon, nearly pure, occurs in charcoal in a 

 solid form, composing all of this substance but the ash. 

 Carbon uniting with the oxygen of the air, forms the car- 

 bonic acid gas, so destructive to animal life when charcoal 

 is burned in a close room. The carbon of plants is derived 

 partly by the absorbtion of carbonic acid gas from the air by 

 their leaves ; but the roots, also, extract a portion of the 

 same gas from the soil. We can increase the supply of this 

 by vegetable manure, such as decayed leaves and other car- 

 bonaceous matters, which, slowly decomposing, supply the 

 roots with abundant food. The others occur only as gases 

 or in combination with other substances. Oxygen forms 

 nearly half the substance of the globe. It unites with hy- 

 drogen, forming eight-ninths of the water we drink; and 

 with nitrogen forming one-fifth of the air we breathe. With 

 carbon it forms the carbonic acid described above. The oxy- 

 gen of plants is derived from all of the above sources, being 

 placed abundantly within the reach of every living thing. 



Hydrogen, in combination with oxygen, forms one-ninth 



