38 CHYMISTRY APPLIED TO AGRICULTtTKE, 



The excrement of the sheep and horse is more heating in 

 its action than that of cows ; the black or brown manures 

 warm the soil more than marl or chalk. 



ARTICLE VI. 



Of the Properties of Mixed Earths, and the Methods of 

 rendering them capable of a good Cultivation. 



I BELIEVE that I have sufficiently explained the origin 

 of soils, their composition, and their influence upon vege- 

 tation ; whether it be exerted through their constituent 

 principles, or by the effects which are produced upon 

 them by air, heat, &lq,. ; it now remains for me to speak 

 of some circumstances which modify soils, and with which 

 the agriculturist ought to be acquainted. 



I have repeated several times in this chapter, and in 

 that in which I have spoken of manures, that the results 

 of the decomposition of animal and vegetable substances, 

 concur with the constituent principles of air and water to 

 form the food of plants ; I have remarked, that plants be- 

 ing immovable, it was necessary that these supplies should 

 be presented to them, and in a state which would admit of 

 their being readily absorbed by the fibres of the plants ; 

 to these observations I have added, that heat animates 

 plants, and gives to their organs the power of decompos- 

 ing these substances, and, from the elaboration of them, 

 of forming all the products of vegetation. 



In order that plants should derive the greatest advantage 

 from their means of support, it is necessary, that their 

 nourishment should be supplied to them in proportion to 

 their wants, and consequently, that the decomposition 

 which the greatest part of these aliments must undergo, 

 should neither be too speedy nor too moderate; the soil 

 appears to be the principal agent in producing these modi- 

 fications, and serves to regulate the others ; it forms a 

 magazine, in which are deposited nearly all the aliments 

 of plants, and it ought to possess all the properties requi- 

 site for supplying the wants of vegetation. 



The characteristics which mark each one of the earths 

 which constitute a soil, concur by their union to produce 

 this effect; chalk and silica retain but little water, but 



