152 PRINCIPLES AND CONCLUSIONS. 



bumble-bees attempted to pierce the leaf with their mandibles, but desisted 

 after several minutes, as the thickness was too great. Finally, two leaf 

 flowers were fastened to the peduncles of simple heads of Dahlia, the one 

 made from the leaf of maple being erect, the other from the currant, 

 hanging. The first received 14 visits, of which 5 were by Bombus, and the 

 second but 4 visits, none of them from bees. 



Incidentally, Plateau made a series of tests with various essences, such 

 as lavender, sage, thyme, mint, etc., but found that they exerted little 

 attraction. Thyme and sage alone afforded a feeble attraction, while the 

 effect of mint was to repel the insects. 



Conclusions as to artificial flowers. — From the above results, Plateau 

 came to the following conclusions : 



(1) In general, the insects observed paid no attention to artificial flowers of bright 



color, whether empty or provided with honey; they even seemed to avoid them. 



(2) In the few cases where they seemed to notice the presence of the artificial flowers, 



they merely hovered about them, a behavior also exhibited before other bodies 

 without any resemblance to flowers. 



(3) The insects did not attempt to enter the flowers made of paper or cloth, even when 



furnished with honey. 



(4) On the contrary, the leaf corollas, marked by the natural plant odor, and normal 



green color, and provided with honey, received numerous visits. 



(5) The attractive influence of bright artificial colors can consequently be regarded 



as practically null. 



General summary. — In completing the series of five papers on the way 

 in which flowers attract insects, Plateau enunciated the following prin- 

 ciples. 



Insects seeking pollen or nectar are guided to the flowers that contain 

 these substances in only a subordinate degree by sight. In fact: 



(1) Neither the form nor the bright colors of flowers seem to have an important 



attractive role. 



(2) Insects visit actively the heads of composites and the umbels of umbellifers not 



mutilated but with the forms and colors masked by green leaves. 



(3) Insects continue to visit flowers or inflorescences in which practically all the bright- 



colored organs are removed, such as petals, corolla, disk-flowers, etc. 



(4) They exhibit neither preference nor antipathy for the different colors afforded 



by the flowers of different varieties of the same species or of related species, 

 passing from a white flower to a blue one, then to purple, rose, etc., without 

 appreciable choice. 



(5) Insects easily discover and actively visit numerous green or greenish flowers, 



which are but slightly visible in the midst of the leaves. 



(6) They ordinarily pay no attention to artificial flowers of paper or cloth, even though 



brightly colored and well-executed, and provided with honey. They even seem 

 to avoid them. 



(7) On the contrary, artificial corollas made of green leaves receive numerous visits 



when provided with honey. 



Insects are guided in an accurate manner to flowers with pollen or nectar 

 by some other sense than vision and this can only be the sense of smell : 



(1) They go without hesitation to those flowers habitually neglected because of the 

 lack or paucity of nectar, just as soon as one provides them with an artificial 

 nectar in the form of honey. 



