SENSIBILITY OF VOLVOX lO SPECTRAL LIGHTS 



351 



percentages of the wave-length of maximum efficiency. The 

 stimulating values thus obtained are to be found in column 5, 

 the curve in figure 1. The band of spectral light with its center 

 at X 494 niM has the greatest stimulating value. The stimulating 

 efficiency of the wave-lengths decrease rapidly and fairly sym- 

 metrically on either side of this wave-length, being the same for 

 X 454 niju and X 534 m^. 



40 



m 



420 440 AfiO 480 500 520 540 560 580 GOO 620 640 e60 mfj. 



Fig. 1 The relative stimulating value of spectral lights of equal energy con- 

 tent as ascertained from the determination of the minimal duration of exposure 

 necessary to produce a reaction. 



Between the application of the stimulus and the initiation of 

 the motor reaction, there is an interval, the reaction time. 

 There is also an interval between the cessation of the external 

 action of the stimulus (i.e., the exposure to the light) and the 

 first evidence of the motor reaction, the latent period, during 

 which the organism need not be illuminated. The reaction time 

 therefore may be divided into two parts: the presentation time, 

 which is the minimal duration of exposure below which no effect 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 30, NO. 3 



