264 The Ohio Journal of Science [Vol. XX, No. 7, 



ar chip pus, Vanessa huntera, V. atalanta, Pholisora catullus, 

 Thymelicus otho egeremet. 



Loew states that Syritta pipiens was caught at the Berhn 

 Botanical Garden, but though this Syrphid was common at 

 Put-in-Bay, none were held by the flowers. 



Bembower (Ohio Naturalist, XI, No. 8, June, 1911, " Polh- 

 nation Notes from the Cedar Point Region") gives a list of ten 

 insects visiting the related species, Apocynum hypericifolium, 

 but does not mention that any were captured by the flowers. 

 Loew, however, noted that 56 flowers of this species in the 

 Berlin Botanical Garden captured 88 small Muscids and 

 Syrphids between early morning and 3 P. M. 



Apocynum pubescens also grows at Put-in-Bay and some 

 observations were made on the flowers for comparison. The 

 blossoms are much smaller and do not open widely, so that it is 

 more difficult for even so small a fly as Mesogramma marginata 

 to enter them. However, a few of them had forced their way in 

 and were held in the same manner. 



In the Journal of Heredity for October, 1917, there is an 

 unsigned article on "The Too-perfect Milkweed" which indi- 

 •cates that "specialization has over-reached the capacities of the 

 organism specialized, and thus the specialization has defeated 

 its own ends." It might appear at first glance that this is true 

 ■of the flowers of Apocynum, for in some cases, at least, the 

 ilowers were so full of Mesogrammas that nothing else could 

 enter, and if these were held on the first attempt to enter, such 

 ilowers would fail to be pollinated. However, it must be stated 

 that in no case was a Mesogramma observed to be held on its 

 first visit, but only after it had entered several flowers. It 

 appears then, that a number of flowers might be pollinated even 

 by this insect, before its proboscis accumulated enough of the 

 sticky secretion or before this secretion evaporated sufficiently 

 to become sticky enough to hold the fly. 



Evidently the Apocynum flower is constructed in such a 

 manner that insects, after reaching the nectaries, must ordi- 

 narily withdraw the proboscis through the slit between the 

 .anthers. At the same time the apparatus fails of perfect adapta- 

 tion in that it does not exclude insects too weak to force the 

 anthers apart. Moreover, to catch these insects defeats the 

 purpose, so to speak, of the mechanism, by preventing, to some 

 extent, the visits of other insects which might be more effective 

 in producing pollination. 



