Growth and Development in the Young Tomato

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Abstract
Tomato seedlings were grown in a 12-hour day at constant and alternating day and night temperatures ranging from 10° to 30° C. The pattern of results was similar at light intensities of 400 and 800 f.c. The maximum rate of dryweight accumulation occurred at a constant temperature close to 25° C. The effects of day and night temperatures on total dry weight showed a considerable degree of independence. The optimum day temperature was 25° C irrespective of the night temperature; the optimum night temperature increased from 18° to 25° C over the whole range of day temperature. On average, day temperature affected total dry weight twice as much as night temperature. High night temperatures to some extent compensated for low day temperatures. The optimum day and night temperatures for leaf growth were both 25° C. On average day temperature affected leaf growth one and a half times as much as night temperature. By 12-hourly sampling it was shown that the cotyledons and leaves grow throughout both day and night and that high night temperature accelerates nocturnal growth (cotyledons by cell expansion, young leaves by cell multiplication). Plants having received only one night at 25° C, as compared with 15° C, show a slightly greater assimilation during the following light period, apparently as a consequence of increased photosynthetic surface. The respiratory loss in dry weight during darkness was not significantly affected by temperature over the range 15–25° C.