Further Experiments on Growth of Excised Root Tips Under Sterile Conditions

Abstract

1. In a twenty-four day period excised corn root tips under sterile conditions make a greater gain in length, and produce more secondary roots in the dark in Pfeffer's solution containing 4 per cent dextrose, than when 0.2, 0.5, 1, 2, or 6 per cent dextrose is present. 2. When the root tip tissue of excised roots is transferred at two weeks' intervals, the gain in the dark in the third period is about the same in Pfeffer's solution containing 2-4 or 6 per cent dextrose. 3. Excised root tips of corn whose original length is 0.35 cm. grow as much, and produce almost as many secondary roots in two periods of transfer, as roots whose average original length is 6 cm. 4. Extracts of corn grains, corn seedlings, corn endosperm, Canada field peas, clover, and metagen were not found to favor the growth of excised corn root tips to any marked degree. 5. Excised root tips of corn in sterile Pfeffer's solution without dextrose may remain capable of growth for twelve days at room temperature in the dark. 6. Excised root tips from grains from the middle of the ear grew somewhat more than those from the tip or butt. 7. Excised root tips of beans, morning glory, alfalfa, mustard, wheat, sunflower, and flax were found to be capable of making considerable growth under sterile conditions in Pfeffer's solution containing 2 per cent dextrose. The results with radish, watercress, squash, and buckwheat were inconclusive. 8. The root tips of white lupine could not be grown in Pfeffer's solution containing various organic materials. One root tip of 90 grew and that to a length of 68 cm.