SPECTRAL COLOR AND STIMULATION 493 



rather weak diffuse daylight. The following da^^ some speci- 

 mens, together with about 2 cc. of clear solution, were taken 

 from this jar, put into the observation aquarium and tested in 

 the spectrum. They were found to orient fairly accurately 

 and to be strongty negative. A series of tests covering differ- 

 ent regions of the spectrum was then made as described in the 

 preceding section. The results obtained in these tests are given 

 in table 2, columns 2-4. 



The following day, August 19, 9 a.m., specimens from the cul- 

 ture jar were tested in nearly pure, clear tap-water as well as 

 in water from the jar. They were negative in both. The tests 

 with the organisms in tap-water were now continued in the 

 spectrum. Toward the close of the series of readings many of the 

 specimens were positive but all of the observations were made on 

 negative specimens. The results obtained in this series of tests 

 may be found in columns 5-7, table 2. By comparing these 

 results with those obtained in the preceding series of tests, it 

 will be seen that they are essentially the same, showing that the 

 impurities in the culture medium, which in most cultures give 

 it a slightly brownish tint, do not appreciably affect the results. 

 All of the following tests, unless other\\dse stated, were made in 

 clear solutions taken from the culture jars. 



On August 20 in the afternoon specimens taken from the cul- 

 ture jar were found to be strongly positive, but toward the close 

 of a series of tests made many of the specimens in the observa- 

 tion aquarium were negative. The results of this series of 

 tests are given in table 3, columns 2 and 3. During the remain- 

 der of the day, specimens were taken from the jar at several 

 different times and tested. They were found to be negative 

 every time, but orientation was not precise enough to obtain 

 accurate readings. The next day, August 21, the euglenae in 

 the jar were again positive and in the afternoon orientation was 

 fairly precise. The results of a series of tests made at this time 

 are presented in columns 4 and 5, and those of another series 

 made with positive specimens, August 23, in columns 6 and 7, 

 table 3. The averages for all of the negative readings and those 

 for all of the positive readings may also be found in these tables 



