. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. FOEM AND AEKANGEMENT OF VESSELS. 17. In their ordinary form, Pleurenchymatous tubes have no definite markings on their walls; but in some instances markings present themselves in the form of simple discs (fig. 48), or of discs with smaller circles in the centre (fig. 49). These discs occur in the wood of Firs, Pines, and Winter's bark, which has received the name of glandular or punctated woody tissue. The markings are formed by concave depres- sions on the outside of
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. FOEM AND AEKANGEMENT OF VESSELS. 17. In their ordinary form, Pleurenchymatous tubes have no definite markings on their walls; but in some instances markings present themselves in the form of simple discs (fig. 48), or of discs with smaller circles in the centre (fig. 49). These discs occur in the wood of Firs, Pines, and Winter's bark, which has received the name of glandular or punctated woody tissue. The markings are formed by concave depres- sions on the outside of the walls of contiguous tubes, which are closely applied to each other, forming lenticular cavities between the vessels, like two watch-glasses in apposition, and when viewed by transmilited light they appear like discs (fig. 48). In the centre of the depression there is a canal, often funnel-shaped, and the part of the tube corresponding to it being thus thinner than the surrounding texture, gives the aspect of a smaller circle in the centre (fig. 49). When a thin section is made through two parallel lines of punctations, the slits or fissures are seen which give rise to the appearances mentioned (fig. 50). That these markings are cavities between the fibres was by Quekett in the case of fossil pine wood, where he separated lenticular masses of solid matter from the discs. There is sometimes observed a thicken- ing layer, in the form of a spiral fibre, surrounding the discs more or less completely, as in the yew. The discs are usually arranged in single rOws, but they occur also in double and triple rows, as in Araucaria, where the markings alternate with each other. Pibeo-Vasculak Tissue, or Trachenchynia (trachea, windpipe; f^, rough), is formed of membranous tubes tapering at each end, less firm than Pleurenchyma, and either having a fibre coiled up spirally in their in- terior, or having the membrane marked with rings, bars, or dots, arranged in a more or les
Size: 1199px × 2084px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
