The Occurrence of Endogenous Rhythms in the Coleoptiles in Various Cereal Genera

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Abstract
The rate of growth of the coleoptiles was determined from photographs taken by infra-red radiation. CO 2 output was measured by means of an infra-red gas analyser. The rhythm of CO 2 output from the coleoptile of Avena was induced by a change from red light to darkness. It has a period of about 24 hours and agrees in timing with the growth-rate rhythm previously recorded. Some degree of rhythmicity in the growth-rate was found in Triticum vulgare (var. ‘Eclipse’) and in Secale cereale (var. Petkus). Very slight indications of rhythmicity were found in Triticum spelta and in Hordeum vulgare . Negative results were obtained with Oryza sativa and with Zea mays . Where rhythmicity in the coleoptile is less strongly developed, the peaks come closer together, the interval being about 18–20 hours. Cereals cannot be sharply separated into two groups according to the presence or absence of rhythmicity in the coleoptile. Of the genera examined, the most marked endogenous rhythms occur in Avena . It is doubtful if the ability of the coleoptile to exhibit an endogenous rhythm has any beneficial effect on the development of the seedling. Under normal conditions of germination induction of the rhythm would not occur.

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