Morphological changes in the shoot apex ofTrifolium repensL.

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Abstract
Cell number, cell size, and mitotic index were measured in specified regions of shoot apices of Trifolium repens. The mitotic indices of the various regions of the apex were closely comparable to their rates of cell division as measured by accumulation of meta phases after colchicine treatment. The mitotic index was significantly higher in flank regions of the apex than in summit, and higher in summit than in rib or axillary regions. The area of the median longitudinal section of the apex was more than doubled during the plastochron; this increase was mainly due to increase in cell number. while mean cell size increased only slightly. The summit region showed no changes in area. cell number, or cell size. The interchange of cells between regions is discussed. There were indications of a cyclic fluctuation in the mitotic index of the nank regions, the mitotic Index increasing to a peak some time before initiation of a primordium on the nank. This may indicate the establishment of a growth centre preceding initiation of the primordium.

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