11 



searches of chemists since 1800, many important facts have been brought 

 to light which have led to improvements in the cultivation of the laud. 



IMPORTANCE OF A PROPER MECHANICAL CONDITION. 



It is not very difficult to adapt the plant or crop to the nature of the 

 soil when once we know what mineral ingredients are required by the 

 one and furnished by the other; but it demands very close observation 

 and study and a most diligent application of means to bring the physi- 

 cal or mechanical properties of the soil into 1he state best fitted for 

 plant growth. 



The influence of mechanical operations become obvious, as the acces- 

 sibility of air, moisture, and warmth, which are essential to the devel- 

 opment of the changes that occur in the process of germination, are 

 but slightly influenced by the chemical composition of the soil, being 

 all dependent on its mechanical condition. And this influence is not 

 confined to the first stages of growth and development of vegetation, 

 but is required all through the life of the plant, for they cannot avail 

 themselves of their full amount of food unless the state of the soil admits 

 of the free passage of air and moisture, and is favorable to the exten- 

 sion of the rootlets in all directions.* 



VARIATIONS IN THE TEXTURE OF SOILS INFLUENCE THEIR FER- 

 TILITY. 



Soils may vary from the coarsest pebbles and loose sands to the finest 

 and most tenacious clays. Those soils are best adapted to agriculture 

 which consist of a mixture of sand with a moderate quantity of clay 

 and a little vegetable matter. When the sand or other coarse material 

 predominates, the soil is easy to till, and will grow most of the crops 

 which are suitable to the locality ; but it is deficient in the power of 

 retaining moisture, and the soluble and volatile parts of manure. W.hen 

 the clay is in excess, the soil is more difficult to till, and will probably 

 grow fewer crops, as it retains more moisture, is not easily warmed, does 

 not admit of free access of air, and consequently does not facilitate the 

 chemical changes in the soil and manure placed on it, which are so im- 

 portant to the proper nourishment of the plants. 



If soils differed in nothing else than that of texture, the one which 

 contained the greatest amount Of finely divided matter would possess 

 an advantage over those with coarser parts. One cause of this supe- 

 riority consists in the greater absorptive and retentive powers which 

 finely divided matter possesses, due probably to the immensely greater 

 quantity of surface exposed in a given bulk or weight of the more finely 

 divided soil.* 



THE ABSORBENT AND RETENTIVE POWERS OF SOIL. 



The observations of Sir H. S. Thompson,! on the absorbent and re- 

 tentive powers of soil, or the power possessed by a soil to decompose 



*The Soil of the Farm. 



t Journal of the Royal Agricultural Society, vol. xi, p. 68. 



