EFFECTS OF HIGH-INTENSITY IRRADIATION 115 



with this filter along with one with the earlier mentioned blue glass 

 filter. The red + infrared cabinet had incandescent lamps and red 

 glass. On the whole, the resuhs fully confirmed and extended those 

 obtained earlier by Stolwijk and Zeevaart. Shoot elongation and flower- 

 ing were rapid in the red + infrared cabinet, and in both blue cabinets. 

 It is of interest and probably of importance that the behavior of the 

 plants does not show any detectable difference in blue light with a 

 small amount of near infrared radiation, and in blue light without 

 detectable traces of near infrared. Elongation and flowering were 

 very much slower in green and red light. Yellow was not used in this 

 series (Fig. 2). 



As for the influence of gibberellic acid, plants were given 0, 0.1, 1, 

 and 10 /xg/plant/day. These additions promoted shoot growth and 

 flowering, increasingly so with increasing concentration. The differ- 

 ence between zero and the highest concentration was somewhat dif- 

 ferent in different spectral regions. The smallest difference between 

 concentrations was in the infrared and in the blue cabinets, especially 

 in the one having a slight admixture of infrared. The greatest difference 

 was in the green and red regions, in which, especially after 30 days, 

 the plants receiving the highest GA concentration were the only ones 

 to show conspicuous elongation, and ultimately (after —60 days) to 

 exhibit flowering. 



Unfortunately, it could not be shown whether GA promotes pri- 

 marily the initiation of flower buds or the elongation, or whether one 

 is a consequence of the other. In all cases examined for this point, 

 the two processes seemed to occur simultaneously. 



The lowest number of days to stem appearance, after the beginning 

 of the colored light treatment, was 13 occurring in the two blues and 

 in red + infrared with 10 ^ig GA/plant/day. The highest number in 

 these colors was 15. In green and red it was 15 with 10 ^^g G A /plant/ 

 day. In green it was 23 with 1.0 /xg GA, and over 30 with 0.1 Mg GA 

 and without GA. In red it was 23 and 25 with 1.0 and 0.1 /xg GA 

 respectively, and >30 without GA. In Fig. 3 are plants given 10 /xg 

 GA and green showing greatly delayed flowering (photographed after 

 68 days). 



A subsequent series of experiments (de Lint, unpublished) included 

 the two different near-infrared cabinets, as mentioned previously. 



