Effect of Photoperiod and Temperature on Development of Barley

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Abstract
4 lots of barley seedlings were grown on 16-hr. photoperiod to ages of 5, 10, 15, and 20 days, respectively, at 65[degree]F. Each lot was then divided into 3 groups and all were grown for another week under the same conditions of light and photoperiod. One group of each lot, however, was continued during the week at 65[degree]F, one was transferred to 45[degree]F, and the 3d to 35[degree]F. The plants were then removed from the control rooms and transplanted out of doors for final differential photoperiodic treatment. At the beginning and end of the temp. treatments representative plants from each lot were photographed and dissected. The total number of nodes in the main axis of each was detd. and enlarged photographs of the terminals of the main axes were made. 10 plants from each age and temp. group were subjected to 12-, 16-, 20-, and 24-hr. photoperiods after they were moved outside and remained on these photoperiods at natural temps. for the duration of the expt. Number of days from planting to awn emergence was detd. At maturity the dry wts. of the tops and of the grain were also detd., and counts were made of the number of seeds per plant. Delay in awn emergence resulted from 12-hr. photoperiod; the younger the seedling at the time of transfer to this photoperiod the greater the delay. Delay in awn emergence resulted from low temp. applied during the seedling stage. The greatest delay occurred when the youngest seedlings were subjected to a week of low temp. and were subsequently grown on 12-hr. photoperiods. Typical temp. after-effects were not observed; the influence of low temp. was expressed through its effect on the growth rate while it was being applied. The plants receiving 12-hr. photoperiod did not produce a single fertile seed, but they produced more dry wt. than the lots receiving longer photoperiods. The 16-, 20-, and 24-hr. photoperiods resulted in lighter plants but all were fertile. Among these 3 lots best yields in number and wt. of seed were obtained from plants on 16-hr. photoperiod. The differences resulting from the photoperiodic treatments have been attributed to the influence upon the plants of low-intensity supplemental light.

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