Bolting and Flowering of Sugar Beets in Continuous Darkness.

Since the discovery by GARNER and ALLARD (3, 4) that day lengtlh is one of the ilmportant factors in flowering, certain plants lhave been classified on the basis of their liglht requirement for flowering as short-day, intermediate, or long-day species. It is reported (6) that all varieties of Beta vulgaris investigated have been found to be long-day plants (1, 4, 6). STOUT (8) states that all beet v-arieties, however, require long plhotoperiods before they will bolt normally, and all varieties may be kept in avegetative condition indefinitely by growing tlhein in an environment of slhort .photoperiods and warm temperature. It lhas been demonstrated repeatedly that sugar beet varieties require a prolonged low-teimiperature exposure before they will bolt. The induction of flowering of sugar beets, under the influence of prolonged low temperatures, lhas been. designated as tlhermal induction. STOUT (9) studied the relation of temperature to reproduction in sugar beets and found that beets bolted more readily following a storage period at 6° C than after storage at lower teimiperatures for the samiie period of time. It was observed that storage near O C induced little clhange in the rate and percentage of bolting indicating that the processes involved in thiermal induction are nearly arrested at this temperature. Reversal of the process was reported to occur in roots that lhad been tlhermally induced previously and then stored at 11 to 260 C. It lhas been pointed out (10) that biennial beets require prolonged exposure to cool temperature (thermal induction) followed by, or concurrent witl, exposures to long plhotoperiods for normial bolting and flowering to take place. Furtlher investigation by Stout led to the conclusion that apparently either long day-lengthi or thermiial induction, acting independently, can carry the reproductive processes far toward completion and that the effects of light and low temperature exposure on reproduction in the sugar beet seem to be complementary. OWEN et al. (6) stated that induction of flowering under the influence of p)rolonged low temperature and long photoperiods may be tentatively regarded as a single process and may tlherefore be designated by a single termii. The termii photothermial induction was proposed by them to cover a broadler meaning because, witlh beets, it was difficult in many cases to distinguish betNeen these two environmental effects. In 1945, the senior autlhor, in connection with biochemical investigations, obtained evidence that if certain of the common sugar beet v-arieties, grown