Elements of plant anatomy; (1895) Elements of plant anatomy; elementsofplanta00greg Year: 1895 ANATOMY OF TISSUES. 47 where cells derived from isodiametric meristem afterward grow long and become prosenchymatic. If there are more than two of these cambium clusters, which is the case in the greater number of dicotyledonous stems, they are arranged in a circle about the stem axis, and are surrounded in all cases by parenchymatic lasting tissue. When they assume the function of meristem they form new walls, mostly parallel with the surface of the stem. It may also be noticed at this stage that t
Elements of plant anatomy; (1895) Elements of plant anatomy; elementsofplanta00greg Year: 1895 ANATOMY OF TISSUES. 47 where cells derived from isodiametric meristem afterward grow long and become prosenchymatic. If there are more than two of these cambium clusters, which is the case in the greater number of dicotyledonous stems, they are arranged in a circle about the stem axis, and are surrounded in all cases by parenchymatic lasting tissue. When they assume the function of meristem they form new walls, mostly parallel with the surface of the stem. It may also be noticed at this stage that they are more or less regularly arranged in tangential rows, and that the new cells are cut off both toward the centra and the cir- cumference. We find these clusters of cambium developing new lasting tissue on two sides, or radially. In this way they become tangential • centres of growth, isolated from each other by the intervening parenchyma. Each one of these cambium clusters with the cells derived from it forms what is known as a vascular hnndle. If this growth is to continue for any length of time, it will be readily seen that, some corresponding change must take place in the cells of the lasting tissue lying between the bundles. If these cells are not to be torn apart and broken by the strain, they must either grow in size to accommodate themselves to the increasing radius, bv they must themselves become meristematic and so originate new cells. This leads to the discussion of a new kind of meristem, which may be called secondary, to distinguish it from that already described as primary. It is one of the characteristics of thin-walled living cells, that they may become fully .differentiated, and take on the properties of lasting tissue, and afterward assume the function Fig. 23. Diagrammatic sketch, cross-sec- tion of herbaceous dicotyledon. g ground tissue, m pith, c vascular bundles. —(fnes?ier.)
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