EFFECTS OF RYANIA AND RYANODINE ON THE APPARENT PHOTOSYNTHESIS OF McINTOSH APPLE LEAVES

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Abstract
The effects of ryania, ryanodine and ryanodine-free-ryania (powdered wood) on the apparent photosynthesis of attached apple leaves have been determined by following the CO2 exchange of the leaves with an infrared gas analyser.After one application, ryanodine decreased photosynthesis by 15 per cent but the photosynthesis had returned to normal within 7 days of treatment. Four applications of ryanodine at 10-day intervals caused no further decrease in photosynthesis than was obtained by a single application.Ryania and powdered wood progressively reduced photosynthesis with each of four applications at 10-day intervals, until photosynthesis was reduced 40 per cent.These results indicate that ryanodine has no marked chemical effect on apple leaves but heavy deposits of either ryania or powdered wood on the apple leaves either shade or interfere with the gas exchange of the leaves.The rates of photosynthesis of untreated apple leaves reached a maximum of 14.95 mg. CO2/dm.2 × hr. when the leaves were 92 per cent of full leaf expansion but had decreased when the leaves were fully expanded and continued to decrease during senescence.

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