380 The Ohio Naturalist. [Vol. XI, No. 8, 



and to one side of the anthers. The stigmatic surface furnishes a 

 convenient Hghting place for insect visitors when they first 

 arrive, thus affecting cross-pollination. 



Visitors: Diptera; Phthiria sulpJiurea, Lucilia caesar; Cole- 



optera; Disonycha pcnnsylvanica; Hymenoptera; 



Agapostemon splendens, Monarda macidata. A 



Bombus, probably B. americana, was observed 



but not taken. 



Rosaceae (Rose Family). 

 Rosa Carolina. A not uncommon plant around the edge of the 

 marsh or around ponds and swampy places. 



Visitors: Diptera; Eristalis americana, Eristalis tenax, Allo- 

 grapta obliqua; Hymenoptera; Agapostemon radi- 

 atus. 



Cactaceae (Cactus Family). 



Opuntia rafinesquii. This cactus, a true Xerophyte, has a yel- 

 low flower that attracts many insects which may efTect either self- 

 or cross-pollination. The filaments are sensitive to mechanical 

 stimulation. They incline inwards on being touched by insects, 

 or ev^en spontaneously, and thickly cover the stigmas with pollen. 

 Autogamy thus regularly takes place and is always effective.* 



In observing the opening of a bud it was noted that within ten 

 minutes after the petals began to separate a visitor (Ceratina 

 dupla) appeared and began delving into the base of the stamens. 

 Here, as well as among some of the other fiow^ers observed, it was 

 noted that while a given insect is visiting certain flowers they 

 usually confine themselves to that species alone, this of course 

 being advantageous in effecting cross-pollination. 



Visitors: Coleoptera, Trichius piger, Strigoderma arboricola, 

 Cciitrinits scutcUum-albnm; Ilymoioptcra; Micro- 

 bembcx monodonta, Agapostemon radiatus, Bom- 

 bus americana, Vespa borealis, Ceratina dupla. 



Cornaceae (Dogwood Family). 



Cornus amomum. "Here the flowers are homogamous with 

 exposed nectar, secreted by a ring st:rrounding the style. The 

 stamens and stigmas develop simultaneously. The anthers are 

 introrse and at the same level as the stigma, though some distance 

 from it. Larger insects will effect cross-pollination while small 

 flies and beetles, owing to their erratic movements, will sometimes 

 effect cross-, sometimes self-pollination."^ 



Visitors: Diptera; Lucilia caesar, Polenia rudis; Coleoptera; 

 Cyrtophorus verrucosus, CryptorJiopalum triste; 

 Hymenoptera; El is plum pies, Polistcs pallipes, 

 Xylocopa virginica, Microbembex monodonta. 



*See Op. cit., II. 45S-459. 

 ^Op. cit., II. 518-519. 



