1. INTRODUCTION AND METHODS. 



INTRODUCTION. 



The original plan for the development of quantitative ecology con- 

 templated two series of monographs, one dealing with the plant in its 

 vegetative relations, the other in its reproductive aspects. The first has 

 received attention in a number of monographs, some of which deal with 

 the individual and some with the community, but the factors and processes 

 involved in the behavior of the flower were necessarily somewhat neglected 

 for a time. Studies of the life-histories of flowers were first begun in 1910 

 and these were followed by observations and experiments upon the relations 

 of flowers and insects. These served to disclose the nature of the problem 

 and to indicate the methods needed for a comprehensive experimental 

 attack upon it. The main investigation was begun in 1918 and has been 

 carried on actively during the succeeding summers. As a consequence 

 the limits of the field have expanded greatly and the present treatment is 

 to be regarded as a preliminary endeavor to organize it upon an adequate 

 experimental and quantitative basis in nature. 



The study of the relations between flowers and insects, begun effectively 

 by Kolreuter (1761) and Sprengel (1793), underwent an enormous expansion 

 at the hands of Delpino (1867), Hildebrand (1867), Mueller (1873), Darwin 

 (1876), Kerner (1876), and Knuth (1894) without becoming experimental 

 in even a small degree. The first investigator to recognize that the great 

 mass of observational results needed to be refined by means of experimental 

 methods was Plateau (1877, 1895), and practically all other experimental 

 studies have been a direct or indirect consequence of his work. 1 The present 

 investigation constitutes the exception, as it was begun with a different 

 objective and with contacts sufficiently slight to permit an independent 

 development of methods. This was of especial importance in view of the 

 comprehensive nature of the plan, as well as in affording a detached view 

 of the methods already employed. This appears to have been justified 

 by the outcome, not only in the matter of methods but also with respect to 

 results and conclusions. Moreover, the difference in objectives has made 

 it possible to plan experiments and interpret results without a bias in favor 

 of Plateau's views or those of his critics. While the relative values of 

 color and odor in attraction constitute one of the most interesting phases of 

 the general problem, they have too long held the center of the stage as a 

 consequence of Plateau's dramatic challenge. However, even in the present 

 case, the adequate analysis and evaluation of the work that has been done 

 make it necessary to treat attraction as the paramount theme. 



This investigation has been carried out at the Alpine Laboratory, which 

 is situated at an altitude of 8,500 feet in the montane forest climax on 

 Pike's Peak. It is perhaps unique in dealing with an insect fauna in exclu- 

 sive contact with a native flora, though some of the experiments have 



1 Since this was written, the admirable monographs of Frisch and of Knoll have become 

 available. These deal almost exclusively with intensive control researches into the response 

 of one or two species to color, odor, or form, and are indispensable to students of experimental 

 pollination. While it is now impossible to abstract them as fully as they deserve, a general 

 account of the methods and results will be found in Chapter 4. 



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