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Recently a large number of tobacco planters in our country make it a rule to cover the seedlings transplanted in the field with polyethylene film or melamine coated paper for several weeks, because the coverings are thought to protect tobacco from the frost and to accelerate the growth on the early period. It seems to promise excellent quality and quantity of yield, but it is not always superior. The essential cause of this fact is that the response of growth to the environmental conditions, especially temperature, affected with those coverings has not yet been made clear. This paper deals with the growth of tobacco under the cover-culture in the natural field, and the following results are obtained. (1) The growth of tobacco is dependent upon temperature affected under the coverings, and accelerated by its increase up to a certain level. At the higher temperature over it the growth is retarded by contraries. This tendency is the same to that on the rate of leaf initiation reported in our previous paper. (2) The age of leaves is influenced indirectly by temperature on the early period. Tobacco accelerated growth makes their leaves mature faster, than that grown under low temperature, but tobacco encounterd higher temperature over an optimum, as it produces many leaves and requires too many days for flower-bud initiation and blooming, delays the maturity of leaves. (3) In the duration from transplantation to the blooming, the ratio of the dry matter weight of each organ to the total is scarcely changed with temperature. This suggests that the response in growth to temperature is not localized in a particular organ but under the high temperature, the total weight per leaf area is reduced. It is thought that it is an adaption to keep the balance between production and consumption of photosynthetic products.

This paper deals with the relationship between tobacco growth and organic matter content of soil in the sand-dune field in Yonago from 1964 to 1966. Results obtained were as follows; (1) The cultivation without manure reduced the yield of fluecured tobacco by about 10% in the non-manured fields for a year, and about 15% in the non-manured fields for two years as compared with the manured fields. (2) Fifty to sixty percent of added organic material was consumed for a year. Consumption of organic matter in the non-manured fields for one year was about 10% less than in the manured fields. Added organic matter in the non-manured fields was consumed perfectly for two years. (3) Organic nitrogen content in the soil varied according to organic matter content, NO3-N in the soil markedly decreased by early summer regardless of manure. The level of NO3-N in the manured soil was slightly higher than those without manure in the latter half stage of growth. (4) In the case without manure, nitrogen and magnesium uptake by tobacco plant were markedly decreased in the latter half stage of growth, and also dry weight of tobacco plant varied in parallel with nitrogen absorption. It is concluded that the manure serves as an important source of mineral nitrogen in the latter half stage of growth.