10 EXPERIMENTAL POLLINATION. 



transposed or the same result obtained by the exchange of stamens. In 

 the great majority of cases, however, addition deals with honey or sugar 

 solutions on the one hand or odorous substances on the other in order to 

 determine the role in attraction. The results with odors depend largely 

 upon whether these are natural ones to which the insects are accustomed 

 to respond and the best method is to employ fragrant flowers or parts 

 regularly visited. 



Competition. — Competition is regarded as natural when plants of two 

 or more species grow so close or intermingled that their flowers compete for 

 the same group of visitors. It is brought about artificially when plants, 

 clusters, or flowers are transferred in such manner as to result in com- 

 petition. The distinction practically disappears when individuals are 

 transplanted or seeds sown in such a way as to form a competition group. 

 Natural competition groups are also constituted when the flowering period 

 of one species is retarded by pruning or cutting back, or accelerated in 

 various ways to cause it to overlap in some degree the period of an associated 

 species. However, when one or more species are transplanted to a different 

 climax or region, the resulting group is more or less artificial in its relations. 

 As a rule, the simplest method is by the transfer of inflorescences or single 

 flowers, which are kept fresh in bottles of water or by means of wet cotton. 

 Clusters have the advantage in saving time and effort and in exerting a 

 stronger attraction for visitors. The best results are obtained when two 

 species are employed reciprocally as bouquet and plant at the same time, 

 but this demands two observers. Mixed bouquets of two or more species 

 or separate bouquets of the same often give good results with a single 

 observer. When visitors are not too abundant, as many as a half-dozen 

 species may be followed at one time if the flowers are close together and not 

 too numerous. Most mutilation experiments are essentially studies of 

 competition between normal and mutilated flowers and it is often profitable 

 to combine these with competition tests between normal flowers of several 

 species. It is especially desirable to have the number of flowers or heads 

 the same for each competitor, and this is secured by basing the number 

 in bouquet or cluster upon that in the group to be used, or by removing 

 flowers to the number desired. Since the standard or species in the natural 

 position is regularly favored in consequence of the habit of the visitors, it 

 is desirable to scatter the competitors through the group, as they may other- 

 wise remain unnoticed. 



Manipulation of insects. — As has been indicated, it is felt that the 

 greatest advance in the study of insect behavior can now be made by 

 dealing with individuals. This not only permits greater accuracy in 

 organizing the results for orders, genera, and species, but it also opens up 

 a new and fertile field scarcely touched as yet. A prerequisite for such work 

 is a simple and rapid method of catching and marking individuals, such 

 as the one devised by Giltay (1906:468). While this will demand still 

 more time and patience, the gain in detail and accuracy over present 

 methods will be as great as that secured by replacing lists of species by a 

 record of visitors and visits. In fact, the actual number of visitors, espe- 

 cially in terms of flight from the nest or hive, can be determined in no other 



