EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 



145 



the hole above the entrance, they swarmed in 6 or 7 at a time and in a 

 moment all had disappeared; it was plainly the color that had directed 

 them. 



Response of wasps to odor. — In studying the attractive effect of 

 odor, the Peckhams surrounded the nest with paper saturated with oil 

 of peppermint or wintergreen. When the latter was employed, a third 

 to a fourth of the wasps noticed the odor, as shown by starting back and 

 circling about. A plate of maple sirup placed 6 inches from the nest re- 

 ceived no attention from the wasps, though visited by many ants and flies 

 and one bumble-bee. Fresh warm chicken bones were wrapped in several 

 thicknesses of gauze of the same color as the paper around the nest and 

 placed 4 inches to one side of the entrance, while a control bundle without 

 bones was put on the other side. In 15 minutes 25 different wasps visited 

 the first bundle, some working over it for a minute or two, but none went 

 to the second. This test was twice repeated with the same results; in the 

 last case 3 wasps worked on the bundle with bones for 15 minutes and then 

 had to be driven away. When the bones were cold, fewer wasps noticed 

 them and only 2 alighted, and 2 days later after they had become dry and 

 relatively inodorous, but 2 out of 129 wasps landed on them. A dead wasp, 

 hidden completely in the grass, attracted 5 others, one of which carried it 

 away. Three or four others afterward visited the spot, probably attracted by 

 the scent of blood. At another time 2 were killed and the ground smoothed 

 over after they had been thrown away; in 15 minutes 9 wasps came to 

 the spot. It was concluded that wasps have a strong sense of smell, but 

 that they pay little attention to odors, however powerful, that do not 

 indicate food. 



MAIN RESEARCHES OF PLATEAU. 

 Masked flowers. — In the first paper of the main series (1895:466), 

 Plateau set himself the task of evaluating the attractive power of color 

 and odor by masking simple heads of Dahlia with colored paper or green 

 leaves. The dahlias grew in a garden with petunias, stocks, nasturtiums, 

 morning-glories, zinnias, phlox, marigolds, etc., all of which were being 

 visited by species of Bombus, Megachile, Vanessa, and Pieris. In the pre- 

 liminary experiments the ray-flowers were covered with squares of paper, 

 red, violet, white, and black in color, the yellow disk projecting through a 

 hole in the center. During an hour the 4 masked heads, which were on 

 different plants, received visits as follows: 



Table 89. 



