RELATED STUDIES AND CRITIQUES. 171 



"Plateau's experiments only show that the sense of smell perhaps guides insects to a 

 greater extent than has hitherto been supposed. Apparently there is need of further 

 experiments to decide questions as to the attraction of insects to flowers by means of 

 the senses of smell and sight. Meanwhile, the following law may be provisionally 

 accepted: Attraction from considerable distances is certainly effected for the most 

 part by the odor of flowers, which fills the air as with invisible clouds and indicates 

 the direction for flight: when the insects approach near (1 to 2 meters), the colors of 

 flowers undertake the task of attracting them further, and when they finally settle, the 

 lines and points long since described by Sprengel under the name of 'Saftmal' (i. e., 

 sapmark) serve to point the way to the nectar." 



Reeker's experiments with artificial flowers. — Reeker (1898:105) 

 made a critical review of Plateau's first series of investigations, in which he 

 brought forward essentially the objections advanced by Kienitz-Gerloff and 

 by Knuth. Of especial interest was an extract from Graber which showed 

 that Plateau was not justified in citing Graber 's views in support of his 

 conclusions, since the latter was actually an exponent of the color sense of 

 insects (p. 215). In the first experiment Reeker employed artificial 

 flowers of Centaurea cyanus, 4 of which were grouped in a square against 

 a green background, at a distance of 6 to 8 meters from other flowers. Dur- 

 ing an hour of observation, 11 individuals of Pieris inspected the imitations 

 and 4 actually alighted. Honey-bees were very scarce, only one coming 

 near the cornflowers, and this landed and probed for nectar for 2 seconds; 

 3 syrphids came to seek pollen and 6 to 8 small flies flitted from one head 

 to another in an assiduous search for pollen or nectar. For the second 

 experiment four artificial flowers of Ranunculus acris were added to the 

 cornflowers in a fairly compact group, placed at a distance of 12 meters from 

 natural flowers. Five Pieris made inspections and 3 others alighted, while 

 one bumble-bee also landed on a cornflower and probed for nectar, and 2 

 honey-bees visited nearly every flower in the group. A dozen small flies 

 made long stays at several flowers and flew back and forth from the blue 

 to the yellow. 



Reeker stated that these experiments gave such uniformly positive results 

 that further investigation seemed unnecessary, an unfortunate conclusion 

 in view of the much more extensive studies of Plateau. He regarded them 

 as furnishing incontrovertible proof that the color and form of flowers serve 

 to attract insects. Granting that the odor of flowers constitutes a very 

 powerful means of attraction, it must also be conceded that color likewise 

 has a share in the attraction of pollinating insects. However, Plateau 

 (1906:87) considered it very probable that the visits noted by Reeker were 

 due to the materials entering into the composition of the artificial flowers, 

 such as starch, etc. 



Decorollate poppies. — In order to demonstrate the importance of the 

 corolla, Giltay (1900) grew Papaver rhoeas in two beds of about equal extent 

 and separated 50 meters from each other, and in a third bed covered by a 

 screen impenetrable to pollinators. In the first two the number of flowers 

 was equalized, and in one the flowers were left to develop normally, while 

 in the other the corolla was removed before the flowers opened. A portion 

 of the latter were later fertilized artificially with other pollen to determine 

 whether the mutilation itself could influence the production of seed. The 



