HOW PLANTS DKINK. 65 



do we really mean by cultivation ? Nothing 

 more than destroying the native vegetation of a 

 place, in order to make room for other plants 

 that we desire to multiply. We plough out the 

 grasses and herbs that occupy the soil ; we sow 

 or plant thinly seeds or cuttings of corn or vines 

 or potatoes that \ve desire to propagate. We 

 give these new plants plenty of space and air - 

 in other words, free access to sunlight and car- 

 bonic acid. And that is the fumHameritar basis 

 of" cultivation to keep down certain natural 

 plants of the place, in order to give free room 

 to others. 



But as the crop-plants require to root them- 

 selves, the farmer naturally thinks most of the 

 soil they root in which he has to buy or rent, 

 while the carbonic acid comes freely to him, 

 unperceived, with the breath of heaven. Where 

 water is scarce, as in irrigated desert lands, the 

 farmer recognises quite equally the importance 

 of water. But he never recognises the true 

 importance of carbonic acid. That is why most 

 people wrongly imagine that plants grow out of 

 the soil, not out of the air. Still, when we burn 

 them, the truth becomes clear. The portion of 

 the plants derived from air and water goes off 

 again into the air in the act of burning : so too 

 does the nitrogen : the remaining portion derived 

 direct from the soil is only the insignificant resi- 

 due returned to the soil as ash when we burn the 

 plant up. 



Nevertheless, the farmer often needs to supply 

 certain raw materials to the soil for the plants 

 5 



