Cultivation of the Orange and Lemon. 105 



plant is burnt, form from one to six per cent, of the 

 plant in its natural condition. 



"The roots not only suck up solutions in water, but 

 also attack solid ingredients of the soil, and they do 

 this by exuding an acid juice which the roots 

 contain. This important function of roots is carried 

 on in different degrees in different plants at the point 

 of contact with the root. This action plays an impor- 

 tant part in the supply of phosphoric acid, potash, 

 lime, and nitrogen to the plant, the latter being taken 

 up in the form of nitrates. 



" The soil is made up of its ' natural strength,' that 

 is, made. up of disintegrated rocks, with the aid of air, 

 moisture, warmth, and frost, and also by the agency of 

 minute bacteria. This action goes on, whether the 

 soil is cultivated or not ; at the same time proper 

 tillage aids the work wonderfully. Even without the 

 latter, the stock accumulates as long as less than it 

 contains is taken. It is in this way that fallow ground 

 recuperates, and that virgin soils have acquired their 

 richness. What the soil will thus do for itself slowly, 

 the gardener may do for it more quickly by manuring. 



" For this purpose we have at command 



" (i.) Stable and farm manure, and refuse of various 

 sorts. 



" (2.) Rubbish of all kinds, ashes, marl, lime, and 

 other cheap materials. 



"(3.) Commercial fertilizers. 



" The first contain all plant food, but are slow in 

 their action. They, however, improve the texture of 

 the soil. 



' The second contain less plant food, but they im- 

 prove the texture of the soil also, and change the 

 dormant constituents of the soil more readily, and turn 

 them into assimilable forms. 



