On the Growth of New Root Influenced by Time of Root-Cutting and Seasonal Changes of Starch Content in the Shoot and Root of Natsudaidai

Three parts of the root of a Natsudaidai of 30 years old on Poncirus Stock were chosen for this test, namely (1) Major root (0.51―1.5cm in diameter), (2) Medium root (0.31―0.5cm in diameter), (3) Minor root (0.10―0.3cm in diameter), and (4) Spring shoot (Shoot of 1 year old and Twig of 2 years old) were selected for the experiment. The roots were artificially cut in the middle of March, June, September and December, and after the elapse of 1 year, these cut roots were dug to check the condition of rooting. On the other hand, roots and shoots were taken up in the middle of each month to make microscopic and chemical observation on the reserve starch at the roots and shoots ^ with the purpose of studying the correlation of the development of root and shoot to the content of starch. The following results were obtained from this research. (1) With regard to the growth of root, the best time for cutting the root to get the best result is, generally speaking, September in the case of Major and Medium roots, March and June being next to it. Those cut in December showed the poorest development. While in the case of Minor roots, the parts cut in March and June develop better in comparison to those cut in December and September. (2) Among Major, Medium and Minor roots, the Majors grow best, being Mediums and Minors next to it. (3) The number of sprouts of Major and Medium roots are from two to seven. Most of the Minor roots have from two to five sprouts. There is not much difference in the length (five to twelve cm.) of sprouts between Major and Medium roots. The majority of Minor roots have the sprouts of ca- 5cm. In comparison to desiduous fruit trees, the number of the sprouts is smaller, and their length shorter, and the rooting of the Poncirus stock seemed to be much affected by root cutting. (4) Growth and development of secondary roots and root hairs are almost the same in Major and Medium roots, though they are poorer in Minor roots. (5) The growth of sprouts stimulated by root-cutting is active during the season from March when the ground temperature rises until September, and is poor in the season of the ensuing December when the ground temperature falls. (6) The content of starch at the root reached its maximum in March-July in Major roots, in March-May in Medium roots, and in April in Minor roots. The minimum was observed in August-October in Major roots, in June-October in Medium roots and in January-March and July-October in Minor roots. (7) No close correlation seems to exist between the quantity of reserve starch in root and the condition of the growth of sprouts after root-cutting.