Photoperiodic Response of Certain Long and Short Day Plants to Filtered Radiation Applied as a Supplement to Daylight.

In a previous publication (4) it was shown that the red portion of the visible spectrum was especially effective in inducing photoperiodic responses in long day plants when used to prolong short winter days. These responses generally included earlier flowering, increased internodal development, and a greater top-root ratio. The yellow, blue, and green regions of the visible spectrum of wavelengths shorter than 650 mp were relatively much less effective. It was further indicated that the infra-red was relatively ineffective under the conditions of experimentation. When the white radiation of an incandescent lamp was used to prolong the normal winter daylight period, the responses obtained were like those produced by red radiation (650 to 720 mpu) alone. Since all of the plants studied in the above mentioned paper were of the long day type, it was considered of interest to determine the spectral region responsible for the vegetative condition induced in typical short day plants as contrasted with the reproductive responses of long day plants, such as occurs when the white radiation of an incandescent lamp is used to prolong the day. SCHAFFNER (3) has shown that corn, which normally produces staminate terminal inflorescence under long summer days, tends to give rise to carpellate flowers in the tassels under the short days of winter, especially when the corn is seeded around the first of November in the vicinity of the latitude of 400 N. Corn might, therefore, be considered a short day plant so far as femaleness in the terminal inflorescence is concerned.