104 



PHOTOCONTROL OF GROWTH 



Fig. 2. The influence of an addition of infrared on the flowering of 

 Salvia occidentalis, grown in 16 hr green light per day. From left to 

 right: plants grown in green light (900 ^w/cm-) without infrared and 

 with 25, 40, or 60 /xw/cm- infrared, 60 days after the beginning of the 

 treatment. 



experiments in which a short day was given in colored light and the 

 long dark period was interrupted. As can be seen in Table III, a long- 

 day effect could be obtained only by a combination of a short day in 

 blue light and a night break with red or green light. 



For Larix leptolepis, it was found also that this spectral dependence 

 existed for the prevention of winter dormancy. Interruptions of the 

 long dark periods were more effective when the plants received blue 

 light instead of red during the preceding short main light period of 10 

 hr. Whereas Larix in this type of experiment shows the spectral 

 dependence for the main light period, it seems justifiable to assume 

 that the negative results in the long-day ( 16 hr) experiments in colored 

 light mentioned earlier must be due to experimental conditions, e.g., 

 the light intensity. For several plant species such as Salvia occidentalis, 

 Poinsettia, Kalancho'e, and Larix, no influence of light quality on the 

 short-day effect could be found. 



A remarkable and unexpected effect was obtained by growing 

 Salvia occidentalis in a short day of 8 hr white fluorescent light per 



