Page:Cellular pathology as based upon physiological and pathological histology.djvu/53

GROWTH OF PLANTS.

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tain intervals and are connected internally with the rows of cells in the cambium. They are structures in which the more delicate forms of cells can best be distinguished, and, at the same time the peculiar mode of growth be discovered. This growth is effected thus : a division takes place in some of the cells, and a transverse septum, is formed; the newly-formed parts continue to grow as independent elements, and gradually increase in size. Not unfrequently divisions take place also longitudinally, so that the parts become thicker (Fig. 8, c). Every protuberance is therefore originally a single cell, which, by continual subdivison in a transverse direction (Fig. 8. a, b), pushes its divisions forwards, and then, when occa- sion offers, spreads out also in a lateral direction. In this way the hairs shoot out, and this is in general the mode of growth, not only in vegetables, but also in the physiological and pathological formations of the animal body.

Fig. 8. Longitudinal section of a young February-shoot from the branch of a syringa. A. The cortical layer and cambium ; beneath a layer of very flat cells are seen larger, four-sided, nucleated ones, from which, by successive transverse division, little hairs (a) shoot out, which grow longer and longer (6), and, by division in a longitudinal direction (c), thicker. B. The vascular layer, with spiral vessels. C. Simple, four sided, oblong, cortical cells. — Growth of Plants.