During the summer and early autumn of 1926, experiments were carried out (Delf, Ritson and Westbrook, 1927) to examine the effects of ultra-violet radiation upon plants. In the course of these experiments a number of widely differing plants (e.g. Trifolium subterraneum, Voandzeia subterranea, Pelargonium, etc.) were exposed for short periods daily to the radiations from a quartz mercury vapour lamp, and observations made upon their growth and structure. It was found that the irradiated plants were stunted, and there was a general tendency for the leaves to become rolled up and distorted; frequently the upper surfaces of the leaves were very shiny, and in many plants the exposed leaf and stem surfaces showed a brown coloration. Anatomical investigation of these plants showed that the epidermal cells had collapsed wherever they had been exposed to rays from the lamp, and the firm dead layer formed by...

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