RELATED STUDIES AND CRITIQUES. 187 



alighted for but a moment. Many, however, rushed about on the disk 

 and some succeeded in passing under the edge or through the opening to 

 the nectaries. In three other flowers the anther column was replaced by a 

 staminate flower of Bryonia and the results were similar, some bees shunning 

 the artefacts and others succeeding after persistent endeavor in finding 

 the nectar. It was concluded that in Anoda triloba the colored corolla is 

 the guide in the flight from flower to flower and that near-flight is deter- 

 mined by optical orientation to color. 



In the case of Bryonia dioeca, flowers provided with a ring of colored 

 paper were readily visited, the visits to the different colors being, yellow 12, 

 blue 8, green 6, and red 1. When the anthers were concealed by colored 

 disks, the visits were fewer than to normal flowers, yellow again leading, 

 and visits continued at about the same rate when the anthers were excised. 

 The complete removal of the perianth greatly decreased the number of 

 visits. The conical disk of three heads of Rudbeckia laciniata was covered 

 with a thin glass tube, with the result that numerous bees flew against 

 the glass, some crawling all over it and others flying about it several times. 

 In two heads the cone was replaced by the similar one of Heliopsis levis; 

 some bees hovered over this and others crawled about on it, but none 

 sipped nectar from it. Heads of Echinacea purpurea placed between those 

 of Rudbeckia were not visited, but they were sought when the disk was 

 replaced by that of Rudbeckia. In order to determine the effect of the yel- 

 low ray-flowers, the cones of two heads were completely removed; bees 

 coming from higher heads or those on the same level paid little attention 

 to these, but those coming from below alighted on them for a moment or 

 darted over the middle. When the disk was covered with blue or yellow 

 paper, bees arriving on the same level or from below alighted on the paper 

 before perceiving their mistake. Bees coming from above visited the green 

 disk after the ray-flowers had been covered with colored paper, but the 

 visits decreased in cases where the rays were all removed. These results 

 were considered to prove that visits are determined by optical signals, 

 and that either ray-flowers or disk suffice for attraction, though the green 

 disk is naturally less effective in this respect. 



From this series of experiments it was concluded that the colored corolla 

 is the normal guide to the individual flowers of a cluster or group, but other 

 guides may be utilized with the result that decorollate flowers may continue 

 to be visited. In consequence no conclusion as to the absence of the color- 

 sense can be drawn from habituated bees. The means of orientation in the 

 flight from flower to flower is optical in nature. Since the different at- 

 tractive parts of the flower can bring about visits when present alone, it 

 is easily seen that partly concealed flowers may be visited. This also ex- 

 plains why the differently colored varieties of a species are visited indif- 

 ferently by bees ; this is possible whenever the flowers agree in the possession 

 of one important guide for the insects, which may be some other part than 

 the corolla. 



Discrimination between similar species of flowers. — In further 

 studies Detto placed clusters of Deutzia flowers in umbels of Crataegus. 

 The bees behaved differently on them, some sipping nectai , others not, but 

 they all flew or crawled to the neighboring flowers of Crataegus. When 



