Holger Jørgensen: The Pollination of Asclepias cornuti Dcne. O 



incarnata is pollinated by humble-bees, just as A cornuti, and 

 its corpuscula are extracted by means of the stiff hairs of the foot 

 of the insect. When an insect flies from A. incarnata over upon A. 

 cornuti, the corpusculum of the latter will get fixed as mentioned. 

 A . incarnata is an American species, which in America grows in the 

 same places, and gets pollinated by the same insects, as A. cornuti. 

 This may probably be the reason of Robertson's observing the 

 corpusculum of A. cornuti upon stiff hairs; for the same thing which 

 is true of the claws is also true of the stiff hairs, viz. that it is impos- 

 sible by experimenting to make corpuscula fix upon them. 



By this it has been made probable that the corpusculum always 

 is fixed upon the pulvillus, presumably because this part of the foot 

 is the only one, which fits in with the fissure of the corpusculum — 

 so that the pulvillus is of vital importance for the extraction of the 

 corpusculum and thus for the pollination. It remains to show how 

 the insect gets the corpusculum fixed upon the pulvillus. A compa- 

 rison between the foot of the insect and the fissure of the anthers 

 proves that the foot of the insect cannot possibly enter into the 

 fissure of the anthers. This becomes the more conclusive, if we con- 

 sider that the pollinating insect always catches hold with extended 

 claws, and this it may be perceived to do. At the outset it might 

 appear to be difficult for the insect to get the corpusculum fixed 

 upon the pulvillus, but the structure of the flower is such that the 

 pulvillus by the movements of the foot of the insect will invariably 

 be passed into the corpusculum. If we pass the foot of an insect 

 upwards upon the flower, in such a way that the two claws pass 

 upon the outside of the fissure of the anthers, while the pulvillus 

 is inside the fissure (vid. Fig. 1), the corpusculum with the pollen- 

 masses will be extracted, and a subsequent microscopic examination 

 will prove the corpusculum to be fixed upon the pulvillus. If we are 

 beforehand familiar with the movement which the insect must make 

 to perform the pollination, we may sometimes see it performed by 

 living insects, especially by such as, for one reason or another, are 

 crawling slowly about upon the flowers. On such occasions we may 

 also see that the insect itself determines whether it will put the pul- 

 villus quite into the stigmatic gland, or remove its foot, before the 

 pulvillus gets as far, so that the term, which several naturalists 

 favour, viz. that the foot is caught in the fissure of the anthers, is 

 not quite correct. 



The pollination of the Asclepias cornuti is consequently, at 

 least in Europe, performed in the following manner. When the polli- 

 nating insects, humble-bees and a few other hymenopters, move 



