Phasic Growth of the Leaves of Cereals

Abstract

DURING some recent experiments on leaf growth, observations were made which do not appear to have been previously recorded in the literature. Initial measurements were made on a potted plant of cape barley (Hordeum vulgare L.) which had been defoliated several times and was growing vigorously in the vegetative phase. A continuous record of leaf elongation was taken in the following manner: a very fine nylon thread was attached to the leaf tip and to the short arm of a thermograph from which the bimetallic element had been removed. The pen arm maintained the leaf in a taut condition and was adjusted to present minimum frictional drag on the lever. The recorder and plant were placed in a draught-free and shock-free position to obtain full autumn sunlight through glass. A continuous record of leaf elongation was obtained covering the weekly thermograph chart by raising the recording unit whenever the lower chart limit was reached. Free water was present in the pot tray at all times during the experiments. This record is illustrated in Fig. 1, in which the original sense of direction of elongation is reversed about the lever fulcrum. The lever magnification was ten times, and the original chart width 3 in.