ROBERTSON FLOWERS & INSECTS, ASCL. TO SCROPH. 597 



(4) B. americanorum F. $ '^ , s. & c.p., ab. ; (5) B. scutellaris Cr. ^, 

 c.p.; (6) iNIelissodes perplexa Cr. 9? c.p.; (7) Ceratina dupla Say 9» 

 s. : (S) Megachile brevis Say 9 ) c.p. ; (9) M. mendica Cr. 9, c.p.; (10) 

 Calliopsis andreniformis Sm. (^'^, s. & c.p. 



Lepidoptera. — Rhopalocera, (11) Pieris rapae L. ; (12) Colias philo- 

 dice Godt. ; (13) Pamphila sp. — all sucking, but mere intruders. 



Halictus confusus Sm. 9 collects stray pollen. Syrpkus americanus 

 Wied. and other Syrphid(Z eat stray grains. Pyrota mylabrhia Chev. 

 (Meloidse) gnaws the petals and anthers. 



Gerardia auriculata Michx. — Resembles G. tenuifolia^ but 

 the corolla is somewhat larger and longer, and the style is not so 

 far advanced in front of the anthers. The narrow part of the tube 

 is about 4 mm. ; but nectar seems to be of little importance, since 

 the flower is visited almost exclusively for pollen. Like most 

 pollen-flowers, it is visited early in the morning, and soon 

 withers. 



On Aug. 30 and Sept. ist I observed as visitors — 



Apidce^ (i) Bombus americanorum F. § , sucks in an upright posi- 

 tion, but reverses to collect pollen; (2) B. pennsylvanicus DeG. ^,s.one; 

 (3) B. virginicus Oliv. i^,s.&c.p.; (4) Melissodes perplexa Cr. 9 > c.p., 

 reversing; (5) Megachile brevis Say 9j s. & c.p., reversing. 



Halictus confusus Sm. 9 collects pollen which falls on the lower lip. 



TJnder the head of "Tipo violaceo" Delpino* includes flowers 

 ■which are so formed that their guests must turn up-side down in 

 order to reach the sweets. As examples he mentions Viola ^ 

 G?'atiola officinalis^ and Epipoguju Gmelini. To this number 

 must be added Gratiola Virginiana^ Gerardia pedicularia^ 

 and probably its allies of the section Dasystoma^ and G. purpu- 

 rea. Viola (and probably Epipogum Gmelini^ has no doubt 

 become fitted to its visitors and then changed to an inverted po- 

 sition, so that the insects must invert also. These inverted flow- 

 ers, therefore, retain their original relations to their pollinators ; 

 Viola still dusts them on the underside, and Epipogum fastens 

 its poUinia on their uppersides. But the Gratiolas and the Ge- 

 rardias originally applied their pollen to the insect's back, so 

 that the form which compels the insect to reverse changes the 

 flower from nototribe to sternotribe. The Gerardias have de- 



* Ulterior! osservazioni. 



