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Plant Growth Under Controlled Conditions. II. Thermoperiodicity in Growth and Fruiting of the Tomato

F. W. Went
American Journal of Botany
Vol. 31, No. 3 (Mar., 1944), pp. 135-150
Stable URL: http://www.jstor.org/stable/2437636
Page Count: 16
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Plant Growth Under Controlled Conditions. II. Thermoperiodicity in Growth and Fruiting of the Tomato
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Abstract

The rate of stem elongation and the setting of fruit of tomato plants, grown in gravel and watered with nutrient solution, is very uniform from plant to plant, from week to week, from season to season, and from year to year, provided they are subjected to the same temperatures. The rate of stem elongation is a sensitive indicator of the effects of different temperatures on the plants, and changes immediately upon change of temperature. The growth rate is not dependent upon the humidity of the air, inasmuch as a decrease in humidity causes merely a temporary decrease, an increase of the relative humidity increases the growth rate only temporarily. When tomato plants are grown in a constant temperature twenty-four hours per day, the optimal temperature lies well above 20⚬C. At 26.5⚬C. a steady growth rate of 23 mm./day is reached when the plants are 30 cm. tall, which rate is maintained as long as the plants are kept trimmed to one stem. Plants grown at lower temperatures have consistently lower growth rates. But plants kept warm during the day (26.5⚬) and cool during the night (17-20⚬) grow more rapidly than any of the other groups (27 mm./day). The lower temperature is only effective when maintained during the dark period. Approximately the same temperature relation holds for fruit development. Fruit set is abundant only when the night temperatures are between 15 and 20⚬; with lower and higher temperatures during the night, fruiting is reduced in amount, or even absent. Artificial light when applied during the cool night period completely inhibits fruit formation. The conclusion is reached that thermoperiodicity in tomatoes is due to the predominance of two different processes at day and at night, of which the dark process has a much lower temperature optimum than the light process. From other work which is discussed, it is suggested that thermoperiodicity is a general phenomenon in higher plants.

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