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UPON THE RATE OF GROWTH 



431 



The foregoing concordant observations may be summed up 

 in the statements that the action of white light upon seedlings 

 is the resultant of the action of the component rays ; that, of 

 these, the red tends to favor growth by rendering possible 

 starch formation ; the blue, on the other hand, tends to 



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FIG. 123. Curves of growth of threads of Bacillus ramosus in hlue light (Experi- 

 ment No. 75, of WARD) and in red light (Experiment No. 74). The numbers at 

 the left indicate microns ; at the bottom, hours. The retardation due to blue 

 light is evident. (From WARD, '95.) 



restrain growth, probably by introducing certain destructive 

 (or controlling) chemical changes ; that, in the dark, seedlings 

 being freed from the restraining action of the chemical rays, 

 grow rapidly so long as the stored food products permit ; that, 

 in daylight, although the means of nutrition is provided, the 

 presence of the inhibiting blue rays tends to cause slow 

 growth. Upon other organisms whose growth is retarded by 

 light, the effect of white and blue light must be quite the same ; 

 and the experiments of VINES and of WARD upon fungi show 

 that this is the case. The effective rays in retardation of 

 growth are clearly those at the blue end of the spectrum. 



