The experiments conducted up to the present day revealed that spraying on the leaves of field-grown tobacco with a solution of transpiration suppressants resulted in the advancement of leaf quality and reduction of nicotine content. The nicotine content in the sprayed leaves is estimated 10-30% lower than that in the non-sprayed ones. Following experiments were con-ducted to find out the cause of the reduction of nicotine content. The leaves of tobacco grown on the field were primed at different 3 ripe stages : immature, mature and overmature stage : after upper and lower surfaces of a half of the leaves Were sprayed immediately after the topping with a solution of a transpiration suppressant. Comparison of nicotine content between the fresh and dry leaves of the non-sprayed and the sprayed leaves showed that the reduction of nicotine content chiefly occured after the leaves attained to mature stage. The reduction of nicotine content in the mature leaves could be detected not only in the sprayed leaves but also in the non-sprayed ones. It is a well known fact in Japan that mulberry leaves which have been stained by evaporated nicotine from the neighboring tobacco field often gives a poisonous influence on the silkworm. The next experiment indicated that, in the leaves which had been kept in N2, much loss of nicotine occurred during the incubation period or after drying of the leaves, whereas, in the other leaves treated with O2, only slight decrease could be detected. The author ascertained, in the other experiment, that the leaves which had been kept in CO2 exhibited higher free nicotine to total nicotine ratio than those which had been kept in the air. Free nicotine is known to be easily evaporated than compound ones. Thus it is probable that the production of free nicotine has an intimate connection with the O2 starvation, in the inner systems of the leaf and the reduction of the content with it's evaporation from the surface of fresh or drying leaves. The loss of nicotine from the non-sprayed leaves might presumably be caused by the O2 starvation due to stomata closure which customally observed after the leaves attained to mature stage. In the sprayed leaves, the surface of the mature leaves with closed stomata would bb covered with the film of the transpiration suppressant. As such a condition of the leaves will prevent the exchange of air efficiently, an advanced O2 starvation would be resulted. This, in turn, will work toward the production of the leaves with lower nicotine levels than those in the non-sprayed ones.
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