PHYSIOLOGICAL RING PATTERN IN SOME GESNERACEAE.

This article presents a study on the cause of physiological ring pattern in some Gesneraceae. From all the experiments it is clear that sudden chilling of the leaves of these plants in sunlight is the cause of the ring and line patterns, and of the more severe total yellowing and necrosis that can be developed. The damage is done almost immediately after contact with the chilling agent, but may not become visible until later. Damage is apparently cumulative, since repeated daily watering under slight shade conditions result in progressively more severe damage, whereas a single watering may have no visible effect. Only slight markings are produced by chilling under conditions of moderate shading, and none occurs under heavier shade. No exact figure can be given for the threshold of light intensity necessary to induce susceptibility, but no markings could be produced in shade conditions where the incident light did not exceed 30 foot-candles.