June, 1911.] Pollination Notes. 381 



Rubiaceae (Madder Family). 

 Cephalanthus occidentalis (Button Bush. This curious plant 

 with flowers arranged in a sperical cluster offers nectar to several 

 species, the only one taken being Eristalis tenax. The Humming 

 Bird previously recorded was also a visitor. 



Compositae (Composite Family). 

 Cirsium arvense (Canada Thistle). Numerous visitors were 

 collected on this Composite, as follows: 



Visitors: Diptera; Odontomyia virgo, Lucilia sericata, Strat- 

 iomyia lalivciitris, Helophilus chrysostomus, Syr- 

 phiis amcricanus, Musciiia assimilis, Eristalis 

 flavipes, Eristalis tenax, Stomoxys calcitrans; 

 Lepidoptera; Chrysophaniis thoe, Argynnis cybele. 



Apocynaceae Dogbane Family). 

 Apocynum hypericifolium. (Clasping-leaved Dogbane). 



Visitors: Diptera; Chrysopus mocreus, Phormia regina, Eris- 

 talis dimidiatus, Stratiomyia lativentris; Lepidop- 

 tera; Argynnis cybele, Chrysophaniis thoe, Hari- 

 sina americana, Alypia octomaculata; Coleoptera; 

 Donacia pusilla; Hymenoptera; Microbembex 

 monodonta. 



Asclepiadaceae (Milkweed Family). 



"In the sub-family Cynanchatae the five filaments are broad- 

 ened, generally fused into a tube, and provided with external 

 appendages, . . . pollen aggregated into polHnia, attached in 

 pairs to the clip glands of the large capitate stigma. The cHps 

 grasp the legs of the insect-visitors when the nectar-secreting spots 

 are on the same radii as the stamens (Asclepias), or the proboscis 

 if these spots alternate with the stamens. . . . The clips are 

 thus drawn out of their recesses by the legs or proboscis of visit- 

 ors, and transferred to other flowers. (Pinch-trap Flowers). The 

 extremely specialized flower mechanisms are adapted to insect 

 visitors in a very perfect manner, so that a comparison may be 

 made with orchids, though in this case there is nothing like the 

 same variety.'"' 



Asclepias. Pinchtrap Flowers. 



Pollination is here effected by the legs of insects. 



Asclepias syriaca. This plant bears flowers of a kind adapted 

 to bees, the claws of which become entangled in the clips and 

 carry off the pollinia to be introduced into the stigmatic chambers 

 of other blossoms. An odor of honey is exhaled. The petaloid 

 appendages of the anthers are in the form of fine fleshy nectar 

 pockets, which alternate with the clips. From the bottom of each 



60p. cit., III. 90. 



