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OF THE SAP-VESSELS.

greater perfection, by Mr. Kniglit, whose papers inthe Philosophical Transactions for 1801, 1804 and1805 throw the most brilliant light upon it, and, Ithink, establish no less than an entirely new theoryof vegetation, by which the real use and functionsof the principal organs of plants are now, for thefirst time, satisfactorily explained.

In a young branch of a tree or shrub, or in thestem of an herbaceous plant, are found, ranged roundthe centre or pith, a number of longitudinal tubes orvessels, of a much more firm texture than the adja-cent parts, and when examined minutely, these ves-sels often appear to be constructed with a spiral coat.This may be seen in the young twigs and leaf stalksof Elder, Syringa , and many other shrubs, as wellas in numerous herbaceous plants, as the Piony, andmore especially many of the Lily tribe. If a branchor stalk of any of these plants be partly cut throughor gently broken, and its divided portions slowlydrawn asunder, the spiral coats of their vessels willunroll, exhibiting a curious spectacle even to thenaked eye. In other cases, though the spiral struc-ture exists, its convolutions are scarcely separableat all, or so indeterminate as to be only marked byan interrupted line of perforations or slits, as shownby M. Mirbel. Indeed the very same brancheswhich exhibit these spiral vessels when young, showno signs of them at amore advanced period of growth,