The cover-culture of tobacco is now spread all over the districts of Japan to get enough quantity of yield and the better qualities of leaves, but occasionally there happens in the cultivation the case in which the tobacco plant produces too many leaves over the moderate level. Consequently it delays maturity of leaves and adversely affects quality of leaves harvested. For removing these defects, it is essential to establish the theory for the technique to regulate number of leaves. Number of leaves of tobacco depends upon the rate of leaf initiation and days for flower-bud initiation affected by temperature and daylength. About environmental factors for the rate of leaf initiation, many investigations suggested temperature was one of the factors, but the reports dealt with tobacco plants in this subject were not found. From these reasons mentiond above, we studied on the relationship between temperature and the rate of initiation of tobacco under the cover-culture in the field. The following results were obtained. (1) The rate of leaf initiation of tobacco is dependent on temperature affected with the coverings. This effects of temperature has two steps; when the temperature rose from low level, leaves were produced faster than would be expected from the prevailing temperature, however when temperature furthermore varied upwards, it decreased the rate of leaf initiation. (2) The border of these contrasting effects is estimated at about 34°C. (3) It is moreover found that when the temperature varied, the rate of leaf initiation was immediately influenced. This fact suggests that the after-effect of temperature scarcely exists for the rate of leaf initiation.
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