The induction, development, and heritability of fasciations . r less is probably owing to the growth in diameter of the stem and to theconsequent tangential stretching- and radial compression of the , these inner cells become elongated in a direction parallel to thesurface, so that their primitive character is wholly lost. In stems 2 mm. in diameter the diameter of the woody cylinder and thethickness of the cortex are noticeably increased as a result of the activityof the cambium. The topography of the chlorophyll apparatus is likewise 14 TOPOGRAPHY OF CHLOROPHYLL APP
The induction, development, and heritability of fasciations . r less is probably owing to the growth in diameter of the stem and to theconsequent tangential stretching- and radial compression of the , these inner cells become elongated in a direction parallel to thesurface, so that their primitive character is wholly lost. In stems 2 mm. in diameter the diameter of the woody cylinder and thethickness of the cortex are noticeably increased as a result of the activityof the cambium. The topography of the chlorophyll apparatus is likewise 14 TOPOGRAPHY OF CHLOROPHYLL APPARATUS IN DESERT PLANTS. somewhat chang-ed, since it has been extended to include the medullary raysof both wood and cortex. The org-anization of the phelloderm, which maybe observed in stems 4 mm. in diameter, also modifies the chlorophylldistribution. The phellogen extends from the outer part of the subepider-mal palisade layer to about the layer of cells which is next to the innerchlorophyll-bearing- cells. In the outer cells the outer ends are converted. Fig. 6.—Ephedra antisyphilitica: A. cross-section of green branch, a detail ofwhich is shown in B. B. portion of stem to show structure of chlorophyll bandof cortex. Foiiquieria spleiideiis: C, transverse section of stem 5 mm. in diameter;bases of stout spines which entirely encircle stem are not shown. D, section ofolder stem in which the chlorophyll band has become discontinuous as a result ofthe stems growth (see text). ^7;. (5., cortical chlorophyll band; earn., cambium. by transverse walls into phellogen; in the inner cells, however, which havethe long axis parallel to the surface in stems of this size, the division wallsforming the i)hellogfen are parallel to the long diameter of the cells. Thebark thus orig-inating- is lens-shaped. It therefore happens that a cross-section of a stem 4 mm. in diameter shows a portion of the primitive cortexwith chlorophyll-bearing- cells and a portion of it converted into cork which
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