Chap. XIL Appendix, Part 4. No. I.

69

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5th, Capillary attraction, or the ascension of water in capil-lary tubes, in which its particles quit the mass, and rise to an in-definite height, in proportion to the smallness and nice construc-tion of the tube. To this, the Rev. Dr Hales erroneously likensthe mysterious ascension of the aqueous sap in growing vege-tables.

Under the dominion of the two first of these laws, water isquite inert; and stagnant water is well known to be the bane ofall land plants, and more especially of those cultivated by man.It is no less injurious to the soil, whatever be its character. Bysoftening cohesive soils, it makes the particles more intimately co-alesce, and become hard as a stone when dry, refusing admissionto vegetable roots. By filling the interstices of porous soils, andits volume swelling with every change of temperature, every ca-vity is enlarged, more stagnant water admitted, and the defect ofthe soil increased ; and thus the roots are chilled in rainy times,and lose their hold on die return of drought.

The three last laws are somewhat analogous in their influence,the affinity of aggregation being broken by them all. Waterbeing then released from its inert state, becomes ambulatory,ranging through the regions -of space. It is under this influencealone that water supports vegetation. In a vapoury state, it pe-netrates the integuments of seeds, softens, swells, and calls tolife the torpid germ. It enters the minute mouths of the roots,mounts, and circulates through all the vessels of the plant, lubri-cating the parts, and carrying along with it the necessary ali-ment in solution. When the sun descends, it visits the externalsurface, suppling the leaves, and fitting them for their peculiarfunctions. Hence we see the great importance of guarding a-gainst stagnant water, and inviting its presence in an ambulato-ry state. For the former purpose, the water must be preventedfrom approaching the surface, if it comes from below; and quick-ly conveyed from the surface, when it comes from above. Forthe latter, the cohesion of the soil must be overcome, and thenumber of interstices increased; but the parts must lie compact,and the interstices between them of the smallest dimensions, soas the ambulatory fluid may freely circulate, and no inert waterlodge.

Water, performing all these important functions, was long be-lieved to be the sole food of plants ; but a due consideration ofthe subject will convince us that it is not. We have seen thatit is composed of two of the ingredients of vegetables, and thesemay be supposed to be drawn from water ; but the third andmost considerable is wanting. Nor is it certain that vegetablesderive these two from the water which they imbibe. It does notappear that the vegetative process has the power of decompos-ing and assimilating water to any sensible extent, since it haskeen amply proved by the able experiments of Dr Hales, and