カブの肥大に関する形態的•組織化学的観察

Abstract

This experiment was carried out to study the thickening of turnips, by morphological, anatomical and histochemical methods.The process of the elongation and thickening of hypocotyl was observed from the morphological point of view, the anatomical changes of hypocotyl from the anatomical method, and the changes of the content of mono- and polysaccharide, nucleic acid and lignin from the histochemical point of view.The results were as follows: The elongation of hypocotyl stopped by the 6th leaf stage in all varieties used, while the beginning of thickening depended upon the variety used. In Yorii-kabu and Kanamachi-kokabu, thickening began at the 4th leaf stage. And at the 6th leaf stage, the thickening of the hypocotyl was visible to the naked eye. But, Koiwai-kabu did not begin to thicken even at its 10th leaf stage.Through the observation of the thickening of turnips, it was found that thickening began from the central part of hypocotyl and after that the thickening of the upper and lower part began. On the other hand, in the case of radishes, the main root was the first to thicken.In anatomical studies on the thickening of turnips, the following was observed: New phloem was formed at the xylem parenchematose tissues, which were situated inside the cambium ring which had been formed by about the 4th leaf stage, and became active. These active cells of the new phloem cut the cambium ring, and as the result, the tissue of the hypocotyl began to thicken. This phenomenon was not observed in other Brassica (B, pekinensis, B. oleracea, B. juncea…).In the histochemical observation of the hypocotyl of turnips even after the 4th leaf stage, the reaction of mono- and polysaccharide and nucleic acid was stronger than in those of non-thickened varieties. On the contrary, the hypocotyl of turnips scarcely showed the reaction of lignin, while the hypocotyl of those which had non-thickened varieties showed a very remarkable reaction.In another observed point of radishes and turnips, the cortex which had formed at their germinating stage was cracked and dropped out when their thickening began. It may be safely said that this phenomenon occurred because primary cortex could not stand the physical changes (thickening) of the inside tissue, which was confirmed both anatomically and histochemically.