The ability of the first internode ofPisum sativumepicotylary axis to produce adventitious roots was examined with respect to dark and light growing conditions and depth position of the soaked seeds in vermiculite. Root initiation began on the 7th day and moved acropetally until the 16th day, with no formation of new roots between older ones. DNA synthesis in the diploid interfascicular cells followed the first mitoses of root initiation. The cell layer that would normally have differentiated into an endodermis reacted more slowly and built a primordial root cap, protecting the root as it grew through the cortex. When the new root emerged a new root cap ndash; protoderm complex was rebuilt from the subapical cells of the root meristem. The increase in cell number was highest during the first 24ensp;h following root initiation, and the cell cycle was extremely short with a very reduced G1phase. Only the elongation zone of the mature adventitious root showed polyploidy.
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