Experimental researches on vegetable assimilation and respiration. XVII.—The diurnal rhythm of assimilation in leaves of cherry laurel at “limiting” concentrations of carbon dioxide

The primary general relation between external supply of carbon dioxide and rate of carbon assimilation in light by the green cells of plants has been investigated by many plant physiologists, and in general, so long as the assimilation is appreciably below the maxima permitted by the light intensity employed and by the temperature of the green cell, the relationship may be held to approximate to direct proportionality between rate of assimilation and external concentration (partial pressure) of CO2 . The case seems most clear for water plants, where a direct proportionality has been demonstrated by Blackman and Smith, 1911 (2), for Elodea. The experiments of Brown and Escombe, 1902 (4), with land leaves, at concentrations of CO2 up to seven times that of ordinary air, point in the same direction, and although the results of later workers with land leaves (Boysen-Jensen, 1918 (3), and Lundegardh, 1921 (7) ), do not in some other respects conform to the simple type shown by the Elodea results, yet, so far as the direct proportionality between CO2 concentration and apparent assimilation is concerned, the position is rather strengthened than otherwise.