II. Experimental researches on vegetable assimilation and respiration.—No. II. On the paths of gaseous exchange between aerial leaves and the atmosphere

On the question of the path by which carbonic acid passes out of the leaf in respiration and into it in assimilation, whether this takes place by the stomatal openings or through the continuous surface of the cuticle, all possible extreme and intermediate views have been expressed in recent text-books of botany. On account of the smallness of the quantities of gas involved, practically no attempt has hitherto been made to determine this question by direct estimation.