The Formation of Starch in Leaves of Bryophyllum Calycinum Cultured in Darkness

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Abstract
An earlier observation that moderate quantities of starch may be formed in excised leaves of B. calycinum collected at dawn and cultured for several days in water in darkness has been confirmed. The increase in starch is accompanied by an extensive and continuous loss of malic acid, and by a slow increase of both citric acid and the group of undetermined organic acids to flat maxima. In addition, about one third of the isocitric acid present disappeared within the first 26 hours. There was a net continuous loss of total organic acids. The loss of organic solids through respiration was rapid for the first 50 hours but subsequently was slow although continuous. The responses of the simple carbohydrates were small in relation to the much larger quantities of organic acids which underwent change. The loss of protein from the tissues was also relatively small. Because of the complexity of the metabolic changes, it is impossible to conclude that the newly formed starch was derived through chemical transformations from the malic acid which disappeared. Nevertheless this remains a possibility. Certain changes in the curves after 75 hours of culture, especially that for starch, are tentatively associated with the initiation of rootlet formation at the indentations of the leaf margin. The observations as a whole indicate the presence in this sp. of a carbohydrate metabolism which is independent of photosynthesis but which can lead to the synthesis of starch.