The Effect of Abnormally Prolonged Alternating Periods of Light and Darkness upon the Composition of Bryophyllum calycinum Leaves

Abstract

Leaves of B. calycinum picked at sunrise were cultured in water in light for 24 hrs, followed by culture in darkness for 24 hrs at room temperature. The behavior of the starch, organic acids, and simple carbohydrates during the first 12 hrs of each of these two periods conformed in general with that to be expected from previous studies of the changes in composition of this tissue when the leaves are exposed to the normal diurnal variation of illumination. However, in the second 12 hrs of each period, the rates of the reactions which affect the starch and malic acid content became very slow and malic acid began to decrease towards the end of the period of darkness. Organic solids increased throughout the light period and for the first 12 hrs of the dark period but then began to decrease. Glucose increased during the first 8 hrs of the light period to a level that was maintained until the last 12 hrs of the dark period, when it again increased. The conclusion is drawn that the time required at room temperature for the major changes in starch and organic acids to occur is rather closely adapted to the period of the normal diurnal variation in illumination. The range through which the concentration of these components may move in response to the diurnal alteration of light and darkness is moderately constant for any given lot of leaves and at ordinary temperature is not increased by prolonged exposure either to light or darkness.