382 S. O. MAST 



EFFECT OF TEMPERATURE ON REVERSION 



In nearly all of the organisms that have been tested increase 

 in temperature tends to induce positive and decrease in tempera- 

 ture negative orientation to light There are only a few forms 

 in which changes in temperature appear to have the opposite 

 effect, but there are a considerable number in which changes in 

 temperature have no effect on the sense of orientation (Mast, 

 '11, pp. 272-279). 



The sense of orientation is probably not specifically related 

 to the temperature in any of the forms studied. For example, the 

 results obtained in observations on Euglena (Mast, '11, pp. 274- 

 277) indicate that this form may be, under certain conditions, 

 negative or positive in practically all temperatures in which it 

 orients at all. 



The effect of changes in temperature on the sense of orienta- 

 tion in Volvox and Pandorina was ascertained as follows: The 

 colonies were mounted on a Pfeifer warming-stage under a bin- 

 ocular. This stage was so arranged that hot or cold water could 

 be passed through it at any rate desired. The whole apparatus 

 was then exposed to constant illumination of the desired intensity. 



The results obtained are in harmony with those obtained in the 

 study of Euglena. The reactions of Volvox were, however, only 

 supei-ficially studied. Without going into details, it may be said 

 that the results clearly show that a rise in temperature tends to 

 produce positive, and a fall in temperature negative photic ori- 

 entations, and that the sense of orientation is not directly de- 

 pendent upon the temperature. For example, in one experiment 

 it was found that Pandorina continuously exposed in a given 

 illumination was, at 10.43 a.m., negative in 16 degrees, neutral in 

 17 degrees, and positive in 18 degrees; at 11.19 a.m., the same 

 colonies were negative in 13.5 degrees, neutral in 14 degrees, and 

 positive in higher temperature, and at 11.28 a.m. they were 

 positive in 14 degrees. Thus the point at which they became 

 positive changed from 18 -degrees at 10.43 a.m. to 14 degrees 

 at 11.28 A.M. 



