SPECTRAL COLOR AND STIMULATION 513 



ditions of the colonies, making it difficult to obtain accurate re- 

 sults in long continued series of tests. The colonies are sometimes 

 negative and sometimes positive, but during the time that they 

 were studied most extensively (July 31 to August 12) they were 

 never found to be very strongly negative, so that satisfactory 

 series of results were obtained only with positive colonies. 



The results of two of the most successful of the series obtained 

 are presented in table 11, columns 5, 6, and 7. By comparing 

 these results with those obtained in Pandorina it will be seen 

 that the distribution in the spectrum of stimulating effect and 

 stimulating efficiency are essentially the same for the two forms 

 mentioned (see table 15). The regions of maximum effect and 

 maximum efficiency appear to be in the same locations in both, 

 and the extent of the effective regions in either direction from 

 these locations appears to be about the same. 



A comparison of the results of all of the tests made, however, 

 indicates that the maximum for Eudorina is slightly nearer the 

 violet than it is for Pandorina. In the 11 series made with 

 .Eudorina the region of maximum stimulating effect was found 

 to be between wave-lengths 534 and 554 /x/j, in all. In 5 of these 

 series it was very near 534 /x/x, in 4 near 544 ^^u, and in 2 the 

 precise location was questionable, while in the 27 series of tests 

 made with Pandorina the region of maximum effect was found 

 to be, as previously stated, near 544 n/j. in 14, near 554 ixfx in 9, 

 near 564 ^t^ in 1, and not precisely located in 2. Thus the 

 maximum was near 534 /x/x in nearly half of the tests made with 

 Eudorina and in none made with Pandorina, while it was near 

 554:ixfjL in one-third of the tests made with Pandorina and in none 

 made with Eudorina. 



Spondylomorum quaternarium 



The colonies of Spondylomorum used in these experiments 

 were collected on August 27 in Michigan near Ann Arbor in a yard 

 frequented by pigs. They were immediately taken to Cleve- 

 land, and during the following three days they were tested from 

 'time to time in various conditions of illumination. In some of 

 the tests traces of acid were added arid the temperature was 



