166 PRINCIPLES AND CONCLUSIONS. 



The results of this series of experiments were summarized in the fol- 

 lowing conclusions: 



1. These observations confirm the fact, already known but not sufficiently empha- 



sized, of the existence of a considerable number of entomophilous flowers of 

 large size and bright color that attract diurnal insects little or not at all. 



2. Two corollaries may be derived from this fact: the first is that the attractive r61e 



of the form and color of the floral envelopes is either null or nearly so; the 

 second is that other causes than the attraction of colored surfaces is necessary 

 to bring pollinators to flowers and to cause them to return, such as an odor pleas- 

 ing to insects and a sugary liquid. 



3. The addition of these two attractions to nectarless flowers that are little visited has 



the practically certain consequence of causing insects to come to them, fre- 

 quently in large numbers. 



4. This type of experiment, previously made by means of honey, succeeds just as 



well when sugar sirup perfumed with an odor properly chosen is employed, a 

 fact which proves that the criticisms directed against the use of honey are 

 not well founded. 



5. To obtain good results it is necessary to avoid the use of most of the pure essences 



of commerce and of artificial perfumes, and to employ substances already known 

 to attract insects, others of which will doubtless be discovered. It is also 

 necessary to work on clear days and during the warmest part of the day, as well 

 as to renew the solution from time to time so that the odor will continue to 

 attract. 



6. The immediate or nearly immediate arrival of insects, not only flies but frequently 



bees as well, at flowers thus treated demonstrates clearly the olfactory sensi- 

 tiveness of insects and, in spite of all the objections raised, proves the import- 

 ance of the role of smell in the attraction of insects by flowers. 



7. In resume^ the present investigation but confirms the thesis advanced in 1S97 in the 



following words: "Insects seeking pollen or nectar are guided to the flowers 

 that contain these substances in only a subordinate degree by sight. They 

 are guided in an assured manner to such flowers by some sense other than 

 vision, and this can only be the sense of smell." 



RELATED STUDIES AND CRITIQUES. 

 Comparative importance of odor and color. — As a consequence of 

 Plateau's first paper, P6rez (1894:245) brought together the results of 

 a number of observations and several experiments to show that both color 

 and odor serve for attraction, as Lubbock had already demonstrated. 

 With reference to the attraction of red flowers, he found that Salvia splen- 

 dens was not visited by honey-bees while in the shade, but as soon 

 as the sun reached it a number of visitors came almost immediately. This 

 was explained as being due to the effect of the sun's rays in favoring the 

 excretion of nectar or freeing its perfume, and not to the greater visibility, 

 but the latter seems much more probable. When honey was placed on 

 the corolla of flowers of a scarlet Pelargonium, honey-bees working on neigh- 

 boring heliotropes were at once attracted by its odor and went directly 

 to the flowers, which they continued to visit until evening. They even 

 returned in the morning, although the honey had been exhausted the eve- 

 ning before, when they also went to flowers that had not received honey 

 and examined them thoroughly. Perez concluded that at a distance where 

 vision could not be an aid, bees and the great majority of insects are di- 



