SPECTRAL COLOR AND STIMULATION 499 



was made (3.39 to 4.02 p.m.). The culture jar was now again 

 placed in weak light and left two days, when specimens taken 

 from it were found to be very strongly positive. The results 

 of a series of tests made at this time are given in table 4, columns 

 5 to 6. The results recorded in the first of these two columns 

 were obtained from tests made in successive order beginning in 

 the green at 534.1 ixjjl and proceeding toward the blue and those 

 in the second column from tests beginning in the violet at 422.4 

 /x/i and proceeding in the opposite direction. 



By comparing these two columns it will be seen that there is a 

 remarkably close agreement between the two series of results 

 obtained, although the two readings in each region of the spec- 

 trum were in no case made successively, and usually there inter- 

 vened a considerable period of time between them. 



These results illustrate the possibiUties of the method em- 

 ployed, but results of such accuracy can be expected only when 

 the organisms are in just the proper condition. The results ob- 

 tained in two series of tests, one for negative and one for positive 

 individuals, not recorded in the table are essentially the same as 

 those recorded, although they are not quite so consistent and 

 accurate. All of these results indicate clearly that the distribu- 

 tion of stimulating efficiency in the spectrum for Euglena gra- 

 cilis is practically the same as it is for Euglena viridis (table 15, 

 p. 521). The region for maximum efficiency is between 473.2 

 and 483.4 ^xjj. near the latter, and from this region the efficiency 

 decreases rapidly toward the red end of the spectrum and more 

 slowly toward the violet end. Moreover, the stimulating effi- 

 ciency for negative individuals appears to be the same as it is for 

 positive ones in both species. 



Euglena tripteris 



One usually finds Euglena tripteris much scattered, a few 

 specimens here and a few there. At Nela Park I was very 

 fortunate in obtaining for a few days, from a fittle water which 

 had collected in a wagon track on a clay road, an abundant 

 supply of these creatures almost pure. 



They were tested in the spectrum from time to time during 

 four days (August 20 to 24) and were found to be almost con- 



