. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. 20 ANATOMY AND PHYSIOLOGY OF Fig. 30. 'INlll jiiiii"'' Mi iraiuiuiii'"'^' fllll jii until'""' h X" .jiiii""" longitudinal growtli, the turns of tlie spiral fibre lie close together (fig. 27); but if the organ undergoes elongation after the completion of the development of the vessel, the turns of the fibre ai^e drawn far apart (figs. 28, 29), by the stretching which the vessel sufiers; consequently, very loosely wound spii^al vessels are usually found in the poster
. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. 20 ANATOMY AND PHYSIOLOGY OF Fig. 30. 'INlll jiiiii"'' Mi iraiuiuiii'"'^' fllll jii until'""' h X" .jiiii""" longitudinal growtli, the turns of tlie spiral fibre lie close together (fig. 27); but if the organ undergoes elongation after the completion of the development of the vessel, the turns of the fibre ai^e drawn far apart (figs. 28, 29), by the stretching which the vessel sufiers; consequently, very loosely wound spii^al vessels are usually found in the posterior first-formed portion of the vascular bundle, nearest to the pith, while those lying nearest the bark have close convolutions. The annular vessds (fig. 30) form a slight modification of the vspiral vessels, for in many cases a series of vascular utricles containing spiral fibres are regularly found followed in the same vessel by a seiies of utricles which contain annular fibres, or spiral fibres and annular fibres alternate without any definite rule, often in the same vessel The reticulated vessels occur in manifold modifications, in particular among the vascular Cryptogamia, and in tlie outer youngest parts of the vascular bundles of the Monocotyledons. In these occurs a dependence of the form and distribution of the pits upon the formation of the adjacent parts, similar to that which we have found in the pitted cells. "When several vessels lie immedi- ately upon one another, the walls by which they are coberent together {^g. 31, a) are covered with trans- verse pits, separated by narrow fibres, and these pits occupy the whole breadth of such a side-wall, but are not continued over the angles at which the several lateral faces of the vessel meet. To this form is applied the term sccdarifofiin ducts. But if the wall of such a vessel is in contact with cells by a large or small surface ^^ ^fibre! ^^^^^ (fig- 3i, 5) its pits exhibit the elliptical or rounded form of the p
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectplantcellsandtissues
