UNICELLULAR FORMS AND COLOR 



327 



respond behind the ruby glass or the potassium bichro- 

 mate solution, and only indefinitely behind the green 

 glass even in direct sunlight. It is therefore evident that 

 the distribution in the spectrum of stimulating efficiency 

 is not the same in these two forms, for the diatoms react 

 only to the shorter waves, while Oscillaria reacts to the 

 longer as well as to the shorter. Whether or not the 

 reaction of Oscillaria to the different rays is proportional 

 to the energy can however not be definitely ascertained 

 from the data at hand. 



4. Experiments of Harrington and Learning on Amoeba 



One of the most interesting of the investigations on the 

 effect of different colors on the reactions of protozoa is 

 that of Harrington and Leaming (1900). These authors 

 projected amoebae on a screen with a Zeiss photomicro- 

 graphic apparatus, and studied the effect of sudden changes 

 in color and intensity on the movements. The light rays 

 were differentiated by means of Bierstadt's colored celloi- 

 din plates. The results of numerous observations, all 

 recorded in detail, are summarized in the following table, 

 which has been slightly modified (p. 16). The table shows 

 clearly that the violet is more effective than any other 

 color tested, except white, in causing retardation in move- 

 ment, and since orientation is the result of such retarda- 

 tions in movement the violet must also be more effective 

 in regulating this phenomenon. 



TABLE X 



Zero indicates that there was no change in movement when the light 

 conditions were changed as indicated; the numbers preceded by — indicate 

 the average time in seconds before streaming stopped or decreased; and the 

 numbers preceded by + indicate the average time before streaming started 

 or increased. 



