. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. Fossil Plants from Fort Grey near East London. 85 presence of large vessels which occur singly or in radially placed pairs. The vessels are surrounded by small thick-walled cells. Medullary rays, 2-4 cells across, traverse the wood (fig. 24). No longitudinal sections are available. The cortex had fibres in groups. Fibres also occur in the phloem, in which the rays widen out. Roots.—Roots of more than one kind have been found, and in some parts are exceedingly abundant. None have been found in con- ne
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. Fossil Plants from Fort Grey near East London. 85 presence of large vessels which occur singly or in radially placed pairs. The vessels are surrounded by small thick-walled cells. Medullary rays, 2-4 cells across, traverse the wood (fig. 24). No longitudinal sections are available. The cortex had fibres in groups. Fibres also occur in the phloem, in which the rays widen out. Roots.—Roots of more than one kind have been found, and in some parts are exceedingly abundant. None have been found in con- nection with a stem, so that identification is not possible. Four types of root can be distinguished. First Type.—These are much the com- monest, indeed they are the commonest fossils. They occur in all the layers. In the lowest, roots are extremely abundant, but are in the form of casts or structure- less tracks. In the hard rock, parts consist of very little else than these roots. The Toots run in various directions, but are FlG> 24.—Dicotyledon most often vertical and at times are very wood, x 105. regularly parallel. There is some variation in size; an average diameter is 2-5 mm., but some are as much as 5-8 mm., and there are many small ones. The smaller ones are often in groups. Branching occurs, but not commonly. In structure the roots have a small central cylinder surrounded by a wide cortex of rather regular parenchyma in regular radial rows. The cells of the cortex appear rectangular in cross-section and have very small or no spaces between. On the outside there are 5-6 layers of smaller cells with thicker walls. In longitudinal view the cortical cells are rectangular and about 2-3 times as long as wide. The central cylinder is bounded by a definite layer which is not distinctly thickened. The centre is filled by the xylem, which is made up of rather small cells, very uniform in size. There are no large vessels. Pith is only found in the largest roots. The xyle
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
