ICO WALL'S MANUAL 



growth, yet one of the conditions essential to it is 

 wanting, namely, heat and light. In addition to the 

 part played by the atmosphere and climate, which 

 may be regarded in a measure as independent of 

 human control, there is a third condition of the 

 growth of plants which relates to the Composition of 

 soils. If there is a want of elements, derived from 

 the soil, growth is impossible; but if they are 

 abundantly supplied, nutrition is rapid, and growth 

 w^ill bo luxuriant. To ascertain and regulate the 

 adaptation of soils to plants, to find out the elements 

 necessary for their development, and the best and 

 most economical method of supplying them, is the 

 great problem of agriculture. This problem we have 

 endeavored to work out in the preceding chapters of 

 this work. We have collected facts, illustrations and 

 experiments from every reliable and available source. 

 In growing cultivated plants, we cannot depend 

 entirely upon the elements of the air. A plant 

 supplied with all the mineral substances in the soil, 

 and allowed sufficient time, will extract the necessary 

 gases from the air, and attain a vigorous develop- 

 ment. But if it is desired to hasten the maturity of 

 the plant, as is frequently necessary in certain 

 climates, or to stimulate it to excessive growth, then 

 vegetable or animal manures must be added to the 

 soil, which, by decay and putrification, generate large 

 quantities of carbonic acid and ammonia in the imme- 

 diate neighborhood of the roots, by which they are 

 taken up when dissolved in water. 



The "ashes " or mineral elements of plants, though 

 small in quantity, yet are of the very highest 

 importance. Unlike the organic elements, which 



