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THE AMERICAN NATURALIST [Vol. XLIII 



few exceptions may be explained by the odor of the 

 evaporating nectar, and by the tendency of bees to return 

 habitually to a place where they have once obtained food. 

 That the white, blue and yellow corollas were beneficial 

 to the flowers of their respective species does not admit 

 of question. To attribute this advantage to any other 

 cause than conspicuousness would appear to be a per- 

 version of the facts. 



Let us again refer to Plateau's experiment with Digitalis 

 purpurea. The larger part of the tubular corolla was 

 cut away leaving a cup-shaped stump 1 cm. long, which 

 was visited by two bees, Bombus terrester L. and An- 

 thidium manicatum L., nearly as frequently as when the 

 flower was complete. Knuth suggests that the nectar 

 now being exposed to the sunshine and wind must evapo- 

 rate more rapidly, give out a stronger odor, and should 

 attract more insects than when it was concealed at the 

 bottom of the long corolla-tube. As this was not the case, 

 he holds that the uselessness of the bright corolla was not 

 proved. I should explain the continuation of the visits 

 of the two species of bees as follows. A cup-shaped 

 flower 1 cm. long is by no means very inconspicuous per se. 

 The bees had already visited these flowers and learned 

 that they contained nectar; and they would come again 

 to the same place in accordance with their well-known 

 custom of returning habitually to a locality where they 

 have once procured food. They would find smaller, more 

 open flowers with perhaps a stronger odor; but that in- 

 sects with the keen discernment of bees should be greatly 

 deceived by this change is highly improbable. The re- 

 sults observed by Plateau in the excision of the corolla 

 of Digitalis purpurea are precisely those which would 

 have been expected. The force of this objection occurred 

 later to Plateau himself in the case of flowers masqued 

 with green leaves, as when he enveloped with the leaves 

 of rhubarb the inflorescence of Heracleum, for he says : 



" Or, j'ai effectue en 1895 et 1896, aux debuts de ma longue serie de 

 recherches sur les rapports entre les Insects et les fleurs, des experiences 



