The microscope and its revelations . ched. Of the purpose ofthese minute bodies interposedbetween the wood-cells, no-thing is known; there can beno doubt, however, from thedefiniteness and constancy oftheir arrangement, that theyfulfil some important object iathe economy of the plants inwhich they occur; and thereare varieties in this arrange-ment so characteristic of dif-ferent tribes, that it is some-tunes possible to determine, bythe microscopic inspection ofa mhiute fragment, even of a fossil wood, the tribe to whichit belonged. The woody fibre thus marked, is often designatedas glandular.
The microscope and its revelations . ched. Of the purpose ofthese minute bodies interposedbetween the wood-cells, no-thing is known; there can beno doubt, however, from thedefiniteness and constancy oftheir arrangement, that theyfulfil some important object iathe economy of the plants inwhich they occur; and thereare varieties in this arrange-ment so characteristic of dif-ferent tribes, that it is some-tunes possible to determine, bythe microscopic inspection ofa mhiute fragment, even of a fossil wood, the tribe to whichit belonged. The woody fibre thus marked, is often designatedas glandular. 232. All the more perfect forms of Phanerogamia contaia,in some part of their fabric, the pecuhar structures which areknown as Spiral Vessels.^ These have the elongated shape of* So long, however, as they retain their original cellular character, and donot coalesce with each other, these fusiform spiral ceUs cannot be regarded ashaving any more claim to the designation of vessels, than have the elongatedcells of the hgneous Section of Coniferous Wood in thedu-ection of the fibres, showing theirglandular dots; a a a, medullaryrays crossing the fibres. SPIRAL VESSELS.—DrCTS. 425 fibres; but the internal deposit, as in the spiral cells228), takes the form of a spiral fibre -winding from end toend, remaining distinct from the ceU-wall, and retaining itselasticity; this fibre maybe single, double, or even quadruple,—this last character presenting itself in the very large elon-gated fibre-cells of the Nepenthes (Chinese pitcher-plant).These cells are especially found in the delicate membrane(medullary sheath) surrounding the pith of Exogens, and inthe midst of the woody bundles occurring in the stem ofEndogens ; thence they proceed in each case to the leaf-stalks,through which they are distributed to the leaves. By carefuldissection under the microscope, they may be separatedentire; but their structure may be more easily displayed, bycutting round, but not through, the
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