PHOTOMORPHOGENESIS 107 



tive effect on the elongation of peas and of Calendula. It was con- 

 cluded by Downs et al. (1957) that the principal effects in their 

 experiments made with blue fluorescent light depend on "relative 

 amounts of red and far-red and not of the blue irradiation." In their 

 experiments, elongation is only connected with the red-infrared antag- 

 onism and an influence of blue light is ignored. It was therefore as- 

 sumed that the elongating effect of blue light found by Wassink et al. 

 and by Vince might not be caused by the blue light itself, but by the 

 presence of traces of near infrared (Meijer, 1957; Wassink et al, 



1957). 



In our laboratory we studied the elongation of many different plants 

 in our light chambers. Plants are grown under natural daylight or 

 white fluorescent light before they are subjected to colored light. The 

 first thing we observed was that species react very differently; there- 

 fore we were able to classify plants into different groups. 



Some plants show a strong elongation of internodes in blue light, 

 whereas they remain short in red and green light or in darkness. Near- 

 infrared irradiation also causes an increase in length. This near-infra- 

 red irradiation was given simultaneously with green light which in 

 itself is ineffective in this respect. A strong red ^ near-infrared antag- 

 onism exists. An addition of near infrared to blue light has hardly any 

 elongating effect. Examples of this group are Petunia, gherkin (Table 

 V), and Calendula. 



Table V. Influence of Light (16 hr per day) of Different Spectral Regions on 



Elongation 

 (Length in millimeters. Intensity of red, green, and blue light: 475 fxw/cm^) 



Duration Spectral Region 



of Treat- — ~ 



ment, Red + Green + Blue + 



Plant Species Days Red Infrared Green Infrared Blue Infrared 



Gherkin 8 23 36 26 101 79 81 



hypocotyl 

 Mirabilisjalapa 30 182 179 174 188 128 153 



first internode 

 Salvia occidenlalis 30 42 60 43 82 64 90 



internode 

 Tomato 11 27 29 24 54 28 42 



hypocotyl 

 Tomato 15 69 74 62 63 38 38 



first internode 



