1. With the aim of studying the physiological mechanisms of the occurrence of the pithy tissue in root crops, various radishes have been investigated as to easiness of its occurrence as well as characters concerned in it.
2. Ones which had a great deal of pithy tissue were found generally in such varieties that the corpulent roots were grown prematurely and also the decrease of T/R ratio was sharp, whereas in the late varieties of which corpulent roots were grown slowly, the occurrence was rather less.
3. From the view-point of internal morphology, the varieties in which the development of internal tissue system accompanied by the corpulency of the roots was rapid and the xylem parenchyma grew and further their cells were large were liable to yield more pithy tissue. On the contrary, the ones which had opposite tendency to the former characters showed less occurrence of it.
4. Generally speaking, the roots of radish which became slowly corpulent contained starch and the high concentration of soluble matter, while the early varieties which had a great deal of pithy tissue contained sugar in place of starch, and their con centration of the soluble matter was less.
5. Regardless of varieties the pithy tissue occurred when the ratio of T/R decreased and on the period when the ratio of leaf weight to the increased value of root weight indicated the minimum, and during the same period the degree of fullness in the root tissue was at the least.
6. The locality and the form of pithy tissue in the roots differed by the varieties, and it is presumed that this is mainly due to the distribution of the conducting tissue of them being different among the varieties.
7. The growth and corpulency of roots being vigorous and their corpulency being carried more abruptly than the assimilative capacity of leaves, the occurence of pithy tissue will be ascribed to the retardation of the fullness of the root tissue.
8. It was seldom to find pithy tissue in such a variety as“Tokinashi”of which the corpulency of its root was rapid and its fullness was good and the greatness of the assimilative capacity of top. seemed to be a big factor at least. At any rate, this kind of radish will offer a useful suggestion in breeding of more resistant varieties to the occurrencee of pithy tissue.
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