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 lativentris, Helophilus chrysostomus, Syr- 
phus americanus, Muscina assimilis, Eristalis 
flavipes, Eristalis tenax, Stomoxys calcitrans; 
Lepidoptera; Chrysophanus thoe, Argynnis cybele. 
Apocynaceae Dogbane Family). 
Apocynum hypericifolium. (Clasping-leaved Dogbane). 
Visitors: Diptera; Chrysopus moereus, Phormia regina, Eris- 
talis dimidiatus, Stratiomyia lativentris; Lepidop- 
tera; Argynnis cybele, Chrysophanus 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 pollinia, attached in 
pairs to the clip glands of the large capitate stigma. The clips 
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 
6 Op. cit., III. 90. 
