108 PHOTOCONTROL OF GROWTH 



Other plants, on the contrary, show a strong elongation in red or 

 ereen lisht and have short internodes in blue light. An addition of 

 near infrared to blue light causes only a slight increase in internode 

 length over the plants in blue light; an addition to red or green light 

 does not have any effect. Plants of this group are Mimbilis jalapa 

 (Table V), Rivina hitmUis, and Mentha longifolia. 



The older internodes of young tomato plants obtain about the same 

 length in red, green, or blue light. An addition of near infrared to 

 blue and green light has a strong elongating effect. The younger 

 internodes, completely grown out in the colored light behave, however, 

 like plants of the second group (Table V). 



As far as blue light has an elongating effect on the internodes of 

 Salvia occidentalis (Table V) as compared with plants grown in red or 

 blue light, this species resembles the plants of the first group. An 

 addition of near infrared to blue light, however, enhances the elonga- 

 tion and in this respect Salvia resembles tomato. 



It may be assumed that the elongation of internodes is controlled 

 by an inhibiting process occurring in red light and another one occur- 

 ring in blue light. In white light both processes take place. In addition 

 to this inhibiting effect, blue light — and to a much greater extent 

 near infrared irradiation — has also a neutralizing influence on the 

 inhibiting effect of red light. This neutralizing influence is only visible 

 when it is stronger than the inhibiting effect of blue light (plants of 

 group 1 and Salvia). In tomato plants and also in plants of the second 

 group, this neutralizing effect of blue light might be completely sup- 

 pressed because the inhibiting effect of blue light is relatively strong. 



REFERENCES 



Borthwick, H. A., S. B. Hendricks, and M. W. Parker. 1952. The reaction 

 controlling floral initiation. Proc. Natl. Acad. Sci. U. S., 38, 929-34. 



Downs, R. J., S. B. Hendricks, and H. A. Borthwick. 1957. Photoreversible 

 control of elongation of Pinto beans and other plants under normal condi- 

 tions of growth. Botan. Gaz., 118, 199-208. 



Funke, G. L. 1948. The photoperiodicity of flowering under short day with 

 supplemental light of different wavelengths. Vernalization and Photoperiod- 

 ism, A. E. Murneek and R. O. Whyte, Editors. Chronica Botanica, Waltham, 

 Mass., pp. 79-82. 



Meijer, G. 1957. The influence of light quality on the flowering response of 

 Salvia occidentalis. Acta Botan. Neerl., 6, 395-406. 



