EFFECT UPOX GENERAL FUXCTIOXS 



177 



between the illumination of the organism and the occurrence 

 of movement. Also, the ultra-red rays produce most rapid 

 locomotion, next the orange-yellow, and weakest the violet-blue 

 and violet-red. Spectrum analysis shows that the most active 

 rays are the ones absorbed by the chromophyll (Fig. 50). 



This phenomenon of phototonus is not confined to the purple 

 bacteria. Thus, FAMIXTZIN ('67, pp. 29-31) has shown that 

 the movements of the closely related Oscillaria are dimin- 

 ished in the dark. SOROKIN ('78) found that protoplasmic 

 streaming in the plasmodium of Dictydium ceases at night, 

 being awakened to movement by the light. Finally, VER- 



a B C 



FIG. 50. a. Spectrum of the chromophyll of bacterio-purpurin, showing absorption 

 bands at A = 0.59 ^ and A = 0.53 /n. An (invisible) absorption band has been deter- 

 mined by means of the bolometer at \ = 0.85 M. 6. The bacteria are seen aggre- 

 gated chiefly in the regions of the absorption bands. The accumulation of bacteria 

 in these regions of absorbed energy seems due to the fact that the moving bacteria 

 cannot pass from a region of high energy to one of low without a violent stimulus 

 which impels them back again. (From ENGELMANN, '83*.) 



X ('89, Nachschrift, and '95, p. 393) finds that, in the 

 dark, the ciliate Pleuronema chrysalis rests quietly in the 

 water, only occasionally making its peculiar spring. But 

 when diffuse daylight is focussed upon it, for instance by the 

 mirror of a. microscope, it springs rapidly by the movement of 

 its long cilia ; and this movement is often repeated, so long as 

 light continues to fall. The movement is produced by blue or 

 violet rays ; red rays have little or no effect. A latent period 

 of from 1 to 3 seconds elapses before the response occurs. 



These cases serve to show that light, in the presence of other 

 suitable conditions, is, both for some chlorophyllaceous organ- 

 isms and plant tissues and for some organisms destitute of 



