[Influence of short-days on arctic plants during the arctic long-days].

In Godhavn (Disko Island, West Greenland) Salix glauca ssp. callicarpaea, Betula nana, Vaccinium uliginosum and Empetrum hermaphroditum in their natural habitat were darkened from 5 p.m. to 9 a.m. daily. The experiment started July 2. At this time the plants were already flowering. After 10 days of this 8-hour short-day treatment the plants showed significant physiological changes compared with the plants in the normal 24-hour long-day: the leaflets of Betula nana showed an autumnal red coloring and the heat resistance (1/2 hours heating, observation 3 days later) of all 4 plants increased by 2-8° C. The frost resistance (24 hours freezing, observation 3 days later) increased significantly in the case of Betula nana. -These experiments seem to indicate that towards the fall the seasonal increase of temperature resistance and other physiological changes in plants are due primarily to the shortening of the day length and only secondarily to the decrease of temperature.