PHOTOREACTION AND ASSOCIATED CHANGES 



looi 1 1 1 1 1 r 



429 



0.1 2 0.3 4 05 0-6 0.7 0.8 9 



Fraction of pigment in for red obsorbing form 



Fig. 3. Internode lengths of pinto beans as a function of pigment con- 

 version. Circles and crosses are for irradiation in the red and far-red 

 parts of the spectrum, respectively, with the pigment initially dominantly 

 in one or the other form. 



the fractional conversion of the pigment is shown in Fig. 3, the meas- 

 urement being the one earher discussed by Dr. Downs. The curve was 

 obtained from four values, two for the reaction with red radiation and 

 two for the reverse. All twelve values, however, fall on the same 

 smooth curve. Similar functions for germination of pepper grass, 

 Lepidium v'lrginicum, and lettuce seed (var. Grand Rapids) are shown 

 in Fig. 4. 



100 



J I \ L 



1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 

 Fraction of pigment in for red absorbing form 



1.0 



Fig. 4. Variation in germination of Lepidium virginiciim seeds and of 

 Grand Rapids lettuce seeds with pigment conversion. The circles repre- 

 sent interpolated values for 50% germination. 



