MANURES. 181 



ammonia. By mould, as I shall use the term, I include only 

 the organic matter distinct from the mineral substances in 

 cohesion with it, and this includes by far . the largest portion 

 in amount and weight of the decomposed matter. This mould 

 of itself, is of great benefit in improving the texture of the 

 soil, in rendering heavy land looser and warmer, and light soil 

 more tenacious. And if it had no other effect it would be of 

 very great value to the land. But when turned by the spade 

 or plough, and exposed to the air, moisture and heat, and acted 

 upon by the mineral substances in combination with it, it 

 becomes gradually still further decomposed, and furnishes 

 continual nourishment both in a liquid and gaseous form to the 

 roots of the plant. It also acts upon the mineral substances in 

 the soil, rendering them soluble, so that they can be received 

 by the plant. The amount of this mould, necessary for the 

 support of vegetation in soils of proper compositions, is com- 

 paratively very small, as such lands may be cropped for a series 

 of years without their becoming exhausted. The comparative 

 value of the mould as food for the plant, has been much 

 considered by scientific men of the present century, and without 

 entering into the discussion it may be sufficient for my purpose 

 to state that all regard it as of very great importance to 

 vegetation. From its intrinsic value as containing many of the 

 elements of the plant, and its slow decomposition, and as a 

 means of improving the texture of the soil it is second in 

 importance to no other material in the soil. In addition to its 

 effects when decomposed to the extent above stated, there is no 

 doubt that in the process of such decomposition it eliminates 

 much that affords nutriment to the plant, particularly of 

 ammonia to which I shall hereafter refer. 



The mineral substances in tlie soil are also necessary, both in 

 affording aliment to vegetation, when dissolved, and as stimu- 

 lants to the soil. They are both indispensable for the proper 

 growth of the plant. 



But in considering the practical value of these nutriments to 

 vegetation, we must always take into consideration the situation 

 of the soil with which they are incorporated, and the exposure 

 to air, heat and moisture to which they are subjected. Land 

 rich in fertilizing matter, yet excessively moist, is unproductive, 

 and grows nothing but sedge and other coarser grasses. The 



