PHOTOMORPHOGENESIS 



103 



Table II. Flowering Response of Salvia occidenlalis to Long-Day Treatment with 

 Different Light Intensities (Duration of treatment, 28 days; day temperature, 22°C; 



night temperature, 17°C) 



The influence of near infrared on the day-length effect was studied 

 in plants growing in 16 hr of green light per day (900 /Aw/cm-); near 

 infrared was added simultaneously by means of incandescent light pass- 

 ing through an infrared filter. Under the experimental conditions, it was 

 found that an amount of ±30 ^w/cm- of near infrared was still 

 effective in causing a long-day effect (Fig. 2). It is obvious that for 

 Salvia Occident alls, a short-day plant, and Hyoscyamus niger, a long- 

 day plant, the same blue-infrared necessity exists to obtain a long-day 

 effect. Other plants also show the same dependence on light quality for 

 the long-day effect, e.g.. Petunia, Arabidopsis thaliana, Plantago 

 major, Silene armeria, and lettuce, all long-day plants. 



Certain other plants, however, e.g., Poinsettia, Kalancho'e, and 

 Xanthium, do not show this spectral dependence, nor does Larix lepto- 

 lepis, in which species a long day in red, green, or blue light always 

 prevents winter dormancy. It is possible that for these plants the light 

 intensity was too high to show the spectral dependence mentioned 

 above. 



Growing Hyoscyamus and Salvia in a short day (10 hr of white 

 fluorescent light per day, 500 /xw/cm-), a long-day effect was obtained 

 by interrupting the dark period. In this process, red light was more 

 effective than blue, and a red-near infrared antagonism existed. The 

 influence of light quality of the short day on the flower-inducing or 

 flower-inhibiting action of such a night break was demonstrated in 



