REVERSION IN ORIENTATION TO LIGHT 385 



Chloroform has the same effect on reversion that acids have, 

 but ether and alcohol have very little, if any effect. With 

 ether, no clear case of reversion was obtained at all, and with 

 alcohol reversion occurred only in colonies that were almost 

 neutral. The concentration of alcohol necessary to kill these 

 colonies, especially Volvox, is very surprising. In equal parts 

 of pond water and 96 per cent alcohol they live for several hours. 



The cause of the effect of anesthetics on reversion is not known, 

 but it is certainly not dependent upon reduction in alkalinity, 

 for the chloroform used was clearly slightly alkaline. This 

 question will be discussed in the following section. 



The evidence presented thus far indicates that the sense of 

 orientation is dependent upon the constitution of the culture 

 medium. This contention is further supported by the fact 

 that ordinarily if colonies are negative in one jar and positive 

 in another in the same illumination, as often happens, the solu- 

 tion in the former is more strongly alkaline than that in the 

 latter. This is, however, by no means always true, and in some 

 instances in which it was found to be true it was also found that 

 the colonies retained their sense of orientation after they were 

 interchanged. That is, the colonies which had been positive in 

 the weaker solution were now positive in the stronger, and those 

 which had been negative in the stronger were now negative in 

 the weaker solution. This demonstrates conclusively that the 

 state of the colonies may determine the sense of orientation. 



DISCUSSION 



It has been demonstrated in the preceding pages that decrease 

 in illumination, decrease in alkalinity, increase in temperature, 

 increase in anesthetics, and increase in the age of the colonies 

 all tend to make them positive. It has also been demonstrated 

 that light-adapted colonies are, under certain conditions, positive 

 in strong and negative in weak light, and that reversion at times 

 depends upon the time-rate of change in illumination. It has, 

 moreover, been demonstrated that the region in the spectrum 

 of maximum efficiency in producing reversion probably coin- 

 cides with that for maximum stimulating efficiency. Reversion 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 3 



