32 



A DISCOURSE 



BOOK I. tions, which being ventilated by glades cut through them, for passage of 

 the stagnant vapours, have been cured of this evil, and recovered their 

 reputation. 



But to return to where we left : Water in this action, imbibed with 

 such matter, applicable to every species of plants and vegetables, does 



liquor, by means of the spittle, pancreatic juice, and bile, before they enter the lacteals, 

 we have all the reason imaginable to keep up the analogy, and suppose that the oleaginous 

 and watery parts of the soil are also incorporated, previous to their being taken up by the 

 absorbing vessels of the plant. To form a perfect judgment of this, we must reflect that 

 every soil, in a state of nature, has in itself a quantity of absorbent earth, sufficient to in- 

 corporate its inherent oil and water ; but when we load it with fat manures, it becomes 

 essentially necessary to bestow upon it, at the same time, something to assimilate the parts. 

 Lime, soap-ashes, kelp, marl, and all the alkaline substances, perform that office. In 

 order to render this operation visible to the senses : dissolve one drachm of Russia pot-ash 

 in two ounces of water ; then add two spoonfuls of oil. Shake the mixture, and it will 

 instantly become an uniform mass of a whitish colour, adapted, as I conceive, to all the 

 purposes of vegetation. This easy and familiar experiment is a just representation of 

 what happens after the operation of Burn-baking, and consequently may be considered as 

 a confirmation of the hypothesis advanced. Let us attend to the process. The sward 

 being reduced to ashes, a fixed alkaline salt is produced. The moisture of the atmosphere 

 soon reduces that salt into a fluid state, which, mixing with the soil, brings about an union 

 of the oily and watery parts, in the manner demonstrated by the experiment. When the 

 under-stratum consists of a rich vegetable mould, the effects of Burn-baking will be lasting. 

 But when the soil happens to be thin and poor, the first crop frequently suffers before it 

 arrives at maturity. The farmer, therefore, who is at the expense of paring and burning 

 a thin soil, should bestow upon it a portion of rotten dung, or shambles manure, before the 

 ashes are spread, in order to supply the deficiency of oily particles. In consequence of 

 this prudent management, the crop will be supported during its growth, and the land will 

 be preserved in health and vigour. Hitherto I have considered plants as nourished by 

 their roots. I shall now take a view of them as nourished by their leaves. An attention to 

 this part of the vegetable system is essentially necessary. Vegetables that have a succulent 

 leaf, such as vetches, peas, beans, and buck-wheat, draw a great part of their nourish- 

 ment from the air, and on that account impoverish the soil less than wheat, oats, barley, 

 or rye, the leaves of which are of a firmer texture. In this manner the vegetable creation 

 i-enders the air pure, by assimilating to itself those putrescent particles, which, if not re- 

 moved, would render the atmosphere unfit for animal respiration. Rape and hemp are 

 oil-bearing plants, and consequently, impoverishers of the soil ; but the former less so than 

 the latter, owing to the greater succulency of its leaf The leaves of all kinds of grain are 

 succulent for a time, during which period the plants take little from the earth ; but as soon 

 as the ear begins to be formed, they lose their softness, and diminish in their attractive 

 power. The radical fibres are then more vigorously employed in extracting the oily par- 

 ticles of the earth, for the nourishment of the seed. 



