12 On the Nourishment produced to the Plant ly its Leaves. 



The ground must be manured by some means. No earth has as 

 much salt and oil as is required for a proper cultivation ; this 

 must be added. — It is hardly possible to conceive the gain of a 

 tviiiter J'ulloii', if the ground is well opened to receive it ; but 

 then it must he free from weeds, that they may not rob the soil 

 of that benefit it would otherwise receive ; and it should be 

 turned over frequently, that the sail m\A juiceshy lying too long 

 above may not evaporate. Poor earths require even more than 

 rich ones ; as wanting it more, it has a greater effect. 



Dr. Dickson, in his most excellent book on Agricultme, ad- 

 vances a proi)osition which I must (though with all humility) dis- 

 sent from. He says, "the red clover affords a large produce of 

 leaf and blossom, on which account the land is kept in a more 

 perfect state of closeness and shade." This I do not deny; but 

 I do the inference drawn from it, when he adds, " it has there- 

 fore much more influence in ameliorating and improving the 

 soil, and affords a better preparation for wheat crops." What 

 is it ameliorates the soil? the bfing shaded from the atmosphere? 

 This is so exactly the contrary, that that nery circumstance makes 

 it a more exhausting crop : if shading from the atmosphere would 

 be sufficient to Ijctter the ground, then a fallow must impoverish 

 it. The earth, the water, and the atmosphere bestow on each 

 alternately nearly the same juices, but the atmosphere is the 

 richest source of gain. If we cover the earth with a vegetable 

 which receives all these bounteous dews, the plants alone profit 

 by it, and the soil possesses not itself of any part. I think 

 the idea must have arisen from some sand plant, such as the 

 turnip ; and the farmer finding that tlie ground was always let- 

 ter, rather than worte, for the crop {though heavy), and not 

 knowing the difference that exists in the quantum of nourish- 

 ment some plants receive from their leaves, concluded that every 

 plant that equally shaded the ground must have the same effect. 

 Now it is a sand plant alone that can do this, taking so little 

 from the root, and of course from tlie soil. If it has very large 

 leaves, it collects so great a quantity of juices from the atmo- 

 sphere, so much more than is sufficient to form the pabulum of 

 the leaves, and the bark jaices, that, running down into the stem, 

 it enters the root, and probably dispenses to the earth that super- 

 ahindancc of nalrimc-nt it could not contain tuithin. But this 

 is far from being the case in other vegetulles ; for all herbaceous 

 plaji':.<!, (which take more than tv.'o-thirds of their support from 

 the root,) if they iiave large leaves, exhaust a ground greatly. 

 Thus rape and hemp can never precede corn or any white crop ; 

 Leciuse they take still more from the ground ; whereas there 

 cannot be a better preparation for wheat than turnips. But I 

 turn again to a fallow, or receiving tliat from the atmosphere 



in$o 



