MAIN RESEARCHES OF PLATEAU. 159 



Evidence of the attractive role of odor. — Plateau properly insisted 

 that the above results did not indicate that the sense of smell played no 

 part in attraction, and he brought forward a number of facts to prove this 

 and in particular the investigations of Mayor and Gorka. 



(1) Flowers that seem to man to have no odor may be shown to possess it by the 



proper method, and these would be perceived by insects with the sense of smell 

 well developed. 



(2) Many champions of the importance of the corolla in attraction have adznitted that 



in certain cases odor can attract insects more strongly than color. 



(3) The apids are much more attracted by odor than is ordinarily believed. Honey- 



bees and bumble-bees seek actively the extrafloral nectar of stipules, petioles, 

 and leaves, while the former, with many flies and wasps, visit fallen and dry 

 fruits. 



(4) The olfactory sense of many insects is extraordinary and guides them from con- 



siderable distances to objects that frequently they can not see, as in the case of 

 saprophilous flies and beetles. Wasps readily find such desired food as cooked 

 meat, and, like bees, are often attracted in great numbers to fruits, preserves, 

 etc. Numerous observations have been made of the attraction from the fields 

 of male moths by a captive female inclosed in a room or in a box. 



(5) Moths are captured at night by means of perfumed sugar solutions placed on 



tree trunks, cords, apples, etc. 



Mayor (1900) clearly demonstrated the unique importance of the sense 

 of smell in connection with the sex attraction in Callosamia promethea. 

 Males of this species when released more than 30 meters from a glass vase 

 covered with mosquito netting and containing 5 females, flew directly to 

 the vase and hovered about the opening. When the vase was inverted in 

 sand so that the females could be seen but no emanation could escape, the 

 males flew away, only to return when the vase was placed again in the 

 original position. When the female was wrapped up in loose cotton, the 

 males flew to the latter and gathered on it. After the females were inclosed 

 in a box with a paper chimney at one end and a lattice at the other, the males 

 flew to the opening of the former, through which the odor was drawn. When 

 the abdomens of the females were detached and placed on a table and the 

 winged thorax placed near by, the males went only to the former. If the 

 antennae of the male were covered with varnish, glue, paraffin, or other sub- 

 stances capable of excluding the odor, it no longer sought the female or 

 even noticed it at a distance of a few centimeters. Plateau pointed out that 

 the experiments of Gorka (1900:57) seemed to demonstrate that odor 

 should be taken into account as well as sight, since the individuals of Deili- 

 phila with the eyes covered with black varnish immediately found the 

 flowers of Borrago and Malta, and shortly afterward, the preferred ones of 

 Phlox. He further stated that, if he had been incorrect in assigning an 

 exaggerated importance to smell, his many observations and experiments 

 proved, as Knuth had admitted, that the sense of smell played a much 

 more important role in the attraction of insects by flowers than had been ad- 

 mitted up to that time. 



Decorollate poppies and insect visits. — In repeating Giltay's experi- 

 ments with flowers of Papaver from which the petals had been removed 

 (p. 171), Plateau pointed out two errors in the method that he regarded 



