184 KANSAS UNIVERSITY SCIENCE BULLETIN. 



each series of observations, under the same conditions of tem- 

 perature, moisture, food and intensity of light, but under 

 different-colored rays, or where the intensity of light was 

 studied under different intensities, for at least three days. 



To ascertain the effect of colored rays, blue, green, yellow 

 and red glass, gelatin films, and reflected rays from Hering's 

 monochromatic colored cards were employed. The observa- 

 tions thus secured were compared with those made in sun or 

 electric light of constant intensity. The colors were placed 

 both in bright and dim light, and so that the reflected or trans- 

 mitted rays penetrated the culture either from above or below. 

 The heat rays were cut out by water contained in parallel-sided 

 glass dishes placed in the path of the beams of light. 



In order to study the influence of the intensity of light, the 

 slides with the vorticella were placed either half or one and a 

 half or two meters from a window having a southern exposure 

 or electric light. Some were placed in a large blackened wall- 

 box or in a box covered with smoked glass to vary the in- 

 tensity of the rays of sunlight. 



From the observations that were obtained from the various 

 experiments, the following general conclusions were deduced: 



1. Vorticella exposed to daylight for intervals of four days 

 increase in number more rapidly on bright sunny days than on 

 dark cloudy ones. 



2. When the zooids are placed at different distances from 

 the source of light on an average 25 develop one-half meter, 

 10 one and one-half meter from the light, and 2 in the dark. 



3. In comparing the greatest number that developed on 

 sunny days from one zooid in 24 hours it was seen that 10 

 grew under green, 29 under yellow, 26 under white, 13 under 

 blue, and 17 under red. 



4. The average rate of increase on cloudy days or under 

 dim light was 4 for yellow, 3 for green, 2 for blue, white or red. 



5. We conclude that the stimulating effect on the repro- 

 ductive power of vorticella increases up to an optimum with in- 

 creased intensity of light, and that the bright, luminous rays 

 of yellow and green are more effective as stimulating agencies 

 on the reproductive power of vorticella than are the red or 

 blue rays. 



