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THE AMERICAN NATURALIST [ Vol. XLIV 



the plain glass slide was invisible, or at least very incon- 

 spicuous. Such a supposition would be a mistake, for 

 while it was certainly less conspicuous than the yellow 

 slip, it could yet be seen clearly by the aid of reflected 

 light and the amber-colored honey at a distance of more 

 than ten feet. A year later on October 11, 1909, this was 

 established by experiment. Two black bees were trained 

 to visit a plain glass slide. While they were absent, the 

 slide was moved six inches to the right, and a blue slide, 

 which owed its color to the floral leaves of the bee-lark- 

 spur {Delphinium elatum) was put in its place. One of 

 the bees returned to the colorless slide. When it left I 

 moved the colorless slide twelve inches to the right of the 

 blue slide. In this position the bees visited it twice. I 

 transposed the slides. Both bees returned to the colorless 

 slide, and a little later one of them came again. As no 

 visits had been made to the blue slide, there could be no 

 question but that the bees saw the plain glass slide. 



As the result of his experiments with artificial flowers 

 Plateau assumes that the artificial colors of paper or of 

 cloth appear to bees of a different tint or tone than do the 

 colors of natural flowers, which to human eyes are ap- 

 parently of the same hue. 6 My own investigations lead 

 me to believe that this assumption is not well founded, 

 and is not required to explain the behavior of bees under 

 the conditions described by Plateau. The discussion of 

 this question, however, would lead to too long a digres- 

 sion from the subject under consideration, and must be 

 deferred to some other opportunity. But in passing it 

 may be remarked that the readiness with which Bethe 

 and his followers assume new forces and powers to sus- 

 tain theoretical positions is not a little amazing to the 

 prosaic naturalist content to work with known factors. 7 



