The occurrence of pithy tissue in root crops. (3)

The influences of culture conditions on the occurrence of pithy tissue

Abstract

1. In order to make the mechanisms of the occurrence of pithy tissue In root crops clear, with the viewpoint of physiology and ecology, the author investigated various culture conditions in relation to the easiness of its occurrence, by us-ing the “Rapid Red” radish.
2. With the aim of comparingg the effect of fertilizer conditions, the test plots which consisted of double complete three elements, complete three elements, non-potassium, non-phosphate, non-nitro-gen, and no fertilizer were adopted. The growth of the radishes was generally excellent in order stated above, and as a rule the presence of nitro-gen compared with other nutrients superiorly promoted the growth of top and root. Pithy tissues were conspicuously abundant in the plots where the growth was vigorous and the root was enlarged rapidly.
3. In the spacing test, the spaced plants, in which the growth, especially corpulency of roots was vigorous and the rate of T/R decreased, show-ed much occurrence of pithy tissue, but on the contrary the densely planted radishes showed op-posite tendency. The plants shaded with reed-blind were inferior in growth, and had less occurrence. The plants which were pruned of half of every leaf decreased the corpulency of roots, while the pithy tissue in them occurred not much less than that in the standard one.
4. To clarify the effect of moisture condition of soil on the-occurrence of pithy tissue, the plant-boxes were divided into wet and dry plot, and the moisture of soil in them were controlled by LIVINGSTON's auto-irrigator. The wet one gave more vigorous growth to the top and root of radishes than those'in the dry plot, and showed the evident pithy tissue.
The plants grown in wet condition in the be-ginning and then conversed to the dry condition at the maximum root corpulent stage, showed a great deal of pithy tissue, but the others which were grown, continuosly in the wet, condition, showed less occurrence. The mechanism of-this occurrence was probably not the same as in the other cases, , being induced by desiccation.
5. In the study of effects of photoperiodism, the longday treatment (about 16 hours a day) restrained the corpulence of the root compared with that of the shortday treatment (about 8 hours a day) or natural day treatment, and it showed less occurrence of pithy tissues. In spite of the fact that there were many bolting plants in the longday plot, it showed less occurrence of pithy tissue, and it is therefore not absolutely true that the bolting itself induced the occurrence of pithy tissue, as commonly considered.
6. In an attempt to study the effects of sowing time on the occurrence of pithy tissue, the seeds were sown 5 times with the interval of 20 days from February 1. Later the sowing time, more vigorously and rapidly the growth of plants was observed, and the occurrence of pithy tissue was greatly hastened. It was not influenced by num-ber of days after sowing or the growing measure of root, but it 'occurred when the corpulency of the root increased and the rate of T/R reached to a certain level. The integrating temperature at the time of occurrence of pithy tissue in all plots was almost alike, but not exactly.
7. With a few exceptions, it was generally concluded that whatever the environmental condi-tions were, a great deal of pithy tissue were found when their growth was vigorous, and the corpulency of roots were rapid: the occurrence of pithy tissue was highly correlated with corpulency of root, smallness of T/R ratio, low concentration of soluble matter in root, and largeness of diameter of xylem parenchyma cells of root as it was explained in the previous two reports. Those results support the author's consideration that the occurrence of pithy tissue may be ascribed to the abrupt growth concerning the corpulency of roots.