176 PRINCIPLES AND CONCLUSIONS. 



appeared as though disconcerted. Osmia tricornis and some males of 

 Anthophora acervorum were not deceived by the change, but one male 

 visited in succession four mutilated clusters before flying away. In the 

 following experiment the colored plume was removed from most of the 

 plants and placed on the ground near normal ones. A female of this species 

 passed by the latter in spite of their fragrance and went directly to one of 

 the detached clusters. However, it quickly recognized its error and de- 

 parted after visiting one of the fertile flowers. These results were thought 

 to confirm the vexillary role of the plume, which was regarded as a better 

 guide than the perfume which diffused in all directions. When the essential 

 organs were excised from flowers of Cistus, such blossoms were visited by 

 Anthophora, in spite of the fact that the fragrance had disappeared, one 

 individual going to three or four after failing to find pollen in the first 

 (cf. Knoll, 1921). 



ForePs experiments with covered dahlias and with artefacts. — 



Forel (1901:26, 1904:22) repeated Plateau's experiments with concealed 

 dahlia heads in order to check his conclusions. A bed of variously colored 

 dahlias, much visited by honey-bees, contained about 43 heads, of which 28 

 were covered with grape leaves fastened below by pins; in 4 heads the 

 yellow center alone was covered, while in a single one the center was free 

 and the rays masked. Forthwith the bees ceased to visit the completely 

 concealed heads, but went to the one with the rays covered just as to the 

 normal. They also flew frequently to the heads with masked disk, but 

 soon forsook them, though a few succeeded in crawling beneath the leaf. 

 Just as soon as the leaf was removed from a red dahlia the bees returned 

 to it, and a poorly covered head was also discovered and visited. Later one 

 bee found an entrance to a concealed head, to which it repeatedly returned. 

 Various individuals continued to seek the dahlias that had so suddenly 

 disappeared and late in the afternoon some of them had discovered the 

 hidden flowers. They were soon imitated by the others and in a short time 

 the concealed heads were again regularly visited. As soon as a bee had 

 discovered the entrance to a masked head, it flew without hesitation to it 

 on subsequent journeys. Single bees were not noticed by the others, but 

 a successful visit by several brought the others after them. It was con- 

 cluded that Plateau's methods were faulty and his results erroneous, due 

 to the fact that he had failed to reckon with the bee's memory and attention. 



Three days later crude imitations of dahlia heads were made by putting 

 yellow Hieracium heads in Petunia flowers and these were placed among the 

 dahlias. Neither Petunia nor Hieracium was visited by the bees, though 

 at first nearly as many flew to the artefacts as to the normal heads. They 

 left them immediately, however, upon finding their error, obviously through 

 the sense of smell. They behaved in the same manner at dahlias with the 

 center replaced by a Hieracium head. As a check a beautiful fragrant 

 dahlia disk was placed among some white and yellow Chrysanthemums 

 neglected by the bees. For a half-hour this remained unnoticed by the 

 many bees, but came to be visited like the normal ones as soon as one 

 or two had discovered it. 



In confirmation of Plateau's results, Forel found that the most carefully 

 made artificial flowers were entirely neglected when placed among the 



