Experimental researches on vegetable assimilation and respiration. VIII.―A new method for estimating the gaseous exchanges of submerged plants

Abstract

The method in universal use for evaluating assimilation in submerged plants consists in counting or measuring the evolution of bubbles of gas. This method gives satisfactory results in medium conditions, but fails at both extremes of the conditions—light, temperature, and CO 2 -supply—which chiefly control the magnitude of assimilation. Critical work over a wide range of conditions is therefore impossible with it. A really satisfactory method must take account of the- alteration of the dissolved gases as well as of those that are liberated as gas-bubbles; because, when assimilation is slight, the oxygen formed may all dissolve in the water and no bubbles appear. When temperature is high the bubbles consist partly of other gases physically liberated from the water, and when the CO 2 -content of the surrounding water is very high the bubbles escaping will consist chiefly of this gas.