Some effects of the photoperiod on growth and pithiness of radishes

Abstract

1. The influence of six different day lengths at 17\dgC on growth and pithiness of two radish varieties was studied. 2. In accordance with earlier investigations bolting gave a clear response to day length. At day lengths of 19 and 24 hours the plants bolted very quickly, at 14 hours more slowly, and at 8, 10 and 12 hours very slowly. 3. There was no direct influence of day length on the degree of pithiness. To some degree there was an indirect influence via the growth rate of the roots as the chance of getting pithy increased with the increase in size of the roots. 4. The number of leaves was essentially the same at all day lengths, but their size increased with longer day length. This evidently was the cause of a higher growth rate of the roots at longer days, in those cases where the bolting condition of the plants had not yet been induced. At the day lengths of 14, 19 and 24 hours the induction of the bolting condition reduced the growth rate of the roots very appreciably.