4. PRINCIPLES AND CONCLUSIONS. 



INTRODUCTORY. 



Nearly the entire history of experimental pollination is reflected in the 

 writings of Plateau and the papers called forth by his results. His were the 

 first researches in this field and for thirty-five years his classic experiments 

 were the outstanding features of its development. Indeed, he and his 

 critics occupied the stage until the last decade, which has been marked by 

 researches not genetically related to his. Thus, while Plateau is the dom- 

 inant figure almost throughout, it is helpful to divide the period of develop- 

 ment into four stages, as follows; (1) early experiments of Plateau and others, 

 (2) main researches of Plateau, (3) related studies and critiques, (4) recent 

 investigations. In the hope of providing a comprehensive and exhaustive 

 account of experimental pollination, abstracts are given in detail of all 

 experimental studies, and of such critical discussions as those of Knuth, 

 Kienitz-Gerloff, and others. Because of their significance and their frequent 

 inaccessibility, the papers by Plateau have been summarized with especial 

 fullness. The historical section is followed by an extended resume of results 

 and conclusions, examined in the light of the present researches. 

 EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 



Artificial flowers. — The stimulus for Plateau's first experiments came 

 from an observation reported by Vallete (1875), according to which an 

 individual of Macroglossa stellatarum, which had entered through the 

 window, tried vainly to plunge its tongue in the flowers of a tapestry, 

 "passing from one bouquet to another and choosing skillfully the flowers 

 that it sought to probe." The unfavorable comments called forth by this 

 statement led Plateau to come to its defense with his study of response to 

 artificial flowers (1877:535). The latter consisted of red and yellow roses, 

 yellow Ranunculus, and variegated Convolvulus, which were made to resem- 

 ble natural flowers as closely as possible. They were placed in the garden 

 among plants of Viola, Pulmonaria, Primula, Fritillaria, Crocus, Hyacinthus, 

 and Arabis, of which the latter was almost alone in being visited by 

 insects, chiefly Vanessa and A pis. During two hours of observation no 

 visitor came to the artificial flowers, though a butterfly passed near one. 

 When the same artificial flowers were placed in a bed of Hyacinthus or of 

 Arabis, or the latter mixed with artificial flowers of its own kind, the results 

 were the same, only a single honey-bee hesitating for a moment above them. 

 Moreover, when a drop of honey was placed in the center of each false 

 Arabis, no visitors alighted on the flowers, although Anthophora frequently 

 poised above them as though drawn by the odor. Two showy beds of arti- 

 ficial flowers of violets, pansies, marsh marigolds, roses, buttercups, etc., 

 were placed in a sunny sward, but of the Anthophora, Apis, Bombus, 

 Pieris, and Vanessa flying about, only the latter noticed them in the least 

 and then but momentarily. On the same day branches of a cherry in full 

 bloom were provided with flowers made to resemble the cherry and white 

 lilac, but the bees visited only the natural ones. When imitation roses, 

 white, pink, and red in color, were mixed with natural ones, Apis, 

 Bombus, Trichius, and various flies showed complete indifference to the 



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