This study was undertaken to see the relation between the amount of transpiration and the development of the vaccular system of Oryza sativa. As the index of the latter the cross sectional area of the vascular portion and number of the vascular bundles at the basal part of the leaf blade were taken, and the former was measured by means of the weighing method, the leaf only being generally used. When the same race cultivated under the same conditions were taken for investigation, the following relation was found: T=kG T ―――― Amount of transpiration per unit leaf area per unit time. G ―――― Ratio of the cross area of the vascular portion to the leaf area. k ―――― Transpiration constant. But such a constant relation cannot be seen when the internal or external conditions are changed; for instance, the relation varies according to different method of cultivation adopted and different races of material used. So far as I have studied, the most important internal factors, concerned here, seem to be the structure, the number and the function of the stomata and the nature of the external wall of the epidermal cells.
1. 蒸騰作用と通導組織の發達には一定の関係あり即ち大體に於て維管束數の大なるもの又は導管部斷面積の大なるものは蒸騰作用大なり, 而して後者と維管束斷面積との相関関係は之と維管束數との間の関係に比して一層密接なるを見る。 2. 導管部の發達以外の他の内的原因が相等しき時與へられたる環境の下に於ける蒸騰相対量は導管部相對面積に正比例するものの如し。即ち T=kG. T : 蒸騰相對量 G : 導管部相對面嶺 k : 面積蒸騰係數 此場合kは實驗的に容易に定め得らる。 3, 他の内的原因が相等しからざる時は兩者間に斯くの如き関係は成立せず,而して此関係を亂す主なる内的原因として氣孔の數・大さ及び作用・表皮細胞外側膜の厚さ等を挙げ得べし。