. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. SECONDARY THICKENING. NORMAL DICOTYLEDONS. 531 the cambium, remained for a long time extremely obscure, and the accurate repre- sentations given by Th. Hartig as early as 1837 failed to be understood, until Mohl, in 1855', brought them into deserved honour. For the same reasons later investi- gations often leave much to be desired, and the special anatomy of the bast is but insufBciently treated of by most authors. Sect. i6z. The main fundamental mass of the medullary rays always consists of par
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. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. SECONDARY THICKENING. NORMAL DICOTYLEDONS. 531 the cambium, remained for a long time extremely obscure, and the accurate repre- sentations given by Th. Hartig as early as 1837 failed to be understood, until Mohl, in 1855', brought them into deserved honour. For the same reasons later investi- gations often leave much to be desired, and the special anatomy of the bast is but insufBciently treated of by most authors. Sect. i6z. The main fundamental mass of the medullary rays always consists of parenchyma. The form and arrangement of its cells are identical with, or very similar to those of the adjacent wood. It likewise occurs in the strands as a constant â¢constituent, and, like the parenchyma of the wood, it is usually derived from single â or repeated transverse divisions of the tissue-mother-cells, in those portions of the cambium which correspond to the strands, and its original arrangement agrees. FIG. 210.âCytisus Laburnum, tangential longitudinal section through the innermost layer of bast of the same branch as Fig. ig8, under the same magnifying power as the latter; ^members of sieve-tubes, i a sieve-plate lying deeper than tlje surface of section, m small medullary ray, two cells in height. The remaining elements are cells of the bast-parenchyma, the origin of which from the transverse division of cambial cells becomes clear on comparison with Fig. 198. FIG. 211, â^Juniperus communis, small stem. Transverse section through the autumnal wood, bast, and cambium, during the winter's rest (end of September); h~h external rows of tht autumnal wood, *, A series of bast-fibres. At x there is only one cambial cell between h and d; mâm medullary rays. with' this mode of development (Fig. 210, comp. also Fig. 198, p. 465); more rarely it arises without transverse division, from longitudinal division only of the tissue-mother-cells, and then corresponds to the inter