Since temperature is an important influence in the activity of most metabolic processes, its influence was examined in some long-day plants, Spinacia oleracea, Brassica, Hyoscyamus niger. If during the dark period respiration were the determining factor, flowering response should increase or decrease with temperature.In spinach, flowering response increased with temperature up to 13°C, in Brassica and Hyoscyamus no such optimum temperature was found.Flowering was, however, promoted in Brassica plants by cold nights at the beginning of the experiment. So several processes interfere in flowering, one of them may be respiration. In long-day plants a short photoperiod in the middle of a long night induced flowering. A temperature of 2°C during this illumination retarded flowering.So the photochemical reaction was closely related to a biochemical one.No relation was found between flowering response and starch hydrolysis during darkness. Sucrose applied to the plant increased flowering response with a day- length of 10 h, while stronger light had no influence.More knowledge of plant biochemistry was required to indicate which processes were involved.
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