1966 Volume 35 Issue 4 Pages 405-412
1. In Japanese maple, Acer palmatum Thunb. var. palmatum (Thunb.), ordinary stem-wood grafting is rarely successful when the shoots of the previous year are used as scion, whereas IHARA and TAMARI (1961) obtained satisfactory results by green wood grafting using the shoots of the current year as scion and stock.
2. To elucidate the cause of the failure in grafting, the effect of temperature on the callus formation was studied with scions of two-year-old seedlings (wild strain) kept on agar media. Graftings were made in different seasons. At the same time, the formation of joining tissues between the scion of a garden variety′Nomura′and the stock of the wild strain was observed for three weeks at different temperatures and different seasons.
3. Little callus formation was observed on the cut surface of scions at low temperatures under 15 °C, while the callus formation was fairly good at 20°C and over, culminating at 30°C. In grafted samples, the. joining tissue scarcely developed under 15°C, while good development was observed at 20°C and 25°C. Most of the scions were, however, covered by moulds and died when incubated at 30°C. The effect of temperature was thus similar in both cases.
4. The younger the age of tissue the better the formation of callus. However, the scions taken from the stem of the previous year formed a considerable amount of callus, which seemed sufficient for successful graft-union.
5. Though good callus formation was observedd at 30°C throughout the year, slightly more callus tissues were formed during the rest period (Jan.-Mar.) than in the growing season (May-Jul.). The graft samples incubated at 2530°C. also resulted in good graft-union at any time of the year, regardless of whether the scions were taken from the shoots of the current year or from the shoots of the previous year and whether they were grafted immediately or after the storage for several months at 5°C.
6. According to these results, inadequate thermall conditions seem to be mainly responsible for the failure of graft-union in ordinary stem-wood grafting of the maple. In trees having the congeniality of grafting, the most effective factor for the union of graft is likely to be the environmental conditions, , especially the temperature.