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



taken that were sufficiently wide open to admit the flies. Of 

 the 100 flowers, 81 contained flies or portions of them. Most 

 of the 19 flowers that had not captured flies appeared very 

 fresh, as though newly opened, and in some cases were, in fact, 

 not yet fully open. Altogether 140 flies had been entrapped. Of 

 this number, 32 were represented by the proboscis only and 21 

 by the heads, leaving 87 complete flies, alive or dead. The two 

 sexes were represented in nearly equal numbers. 



Knuth's Handbook of Flower Pollination, (translation by 

 J. R. Ainsworth Davis, 1909, Vol. Ill, pp. 88-89), gives a very 

 good account of the Apocynum flower and its method of pol- 

 lination, quoted from Ludwig (Bot. Centralbl., Cassel, VIII, 

 1881, pp. 184-185). The anthers are stiff and are united to the 

 bulbous style at about their middle. The lower half of the 

 bulb bears the stigmatic surface, below the attachment of the 

 anthers, while the pollen sacs open above the attachment. In 

 pollination, the insect, in search of nectar, thrusts in its pro- 

 boscis in such a manner that, to withdraw it, it must pull it 

 upward between the edges of the anthers, and in so doing the 

 proboscis comes into contact with the pollen. Then in visiting 

 the next flower the pollen is brought into contact with the 

 stigmatic surface. But for insects which are too weak to with- 

 draw the proboscis properly, this arrangement forms what has 

 been called a "pinch trap." 



Ludwig discusses this pinch trap, as observed by him, and 

 indicates the insects noted by Loew to have been caught by 

 Apocynum afidroscemifolium in the Berlin Botanical Garden. 

 But one thing Ludwig failed to notice, or perhaps it was not 

 shown in the flowers examined by him. Some of the flies are 

 not held between the edges of the anthers at all, but are stuck 

 fast on the outer surface of the anthers and, in one case observed, 

 on the inner surface of the corolla. 



There is therefore, another factor, not hitherto noted, in the 

 process of entrapment, namely, the adhesive nectar. The 

 presence of this factor is borne out by the behavior of the flies 

 at work. Mesogrammas coming to a flower cluster were often 

 seen to enter and emerge without difficulty for several times, 

 but, as the same individual was watched, it would eventually 

 be caught. Sometimes after a little difficulty, one would pull 

 loose, but only to enter another flower, as though definitely 

 bent on this particular form of suicide, when it would be per- 



