1896] FLOWERS AND INSECTS 155 
flowers of like color and nectar exposure, we might expect a 
strong predominance of flies. My observations do not show 
this. 
With the exception of no. 18, taken April 23d, the following 
list was observed on May Ist: 
HYMENOPTERA — Andrenide : (1) Halictus confusus Sm. ¢,s. & c. p.; (2) 
H. 4—maculatus Rob, 9, s.: (3) Augochlora viridula Sm. 9, s.; Braconide : (4) 
Bracon trifolii Ashm.; (5) B. veronniz Ashm.: (6) Microgaster gelechiz Riley, 
ab.; (7) Opius ruficeps Proy.; (8) Dacnusa flavicincta Ashm.; Chalcidide : 
(9) Prosacantha illinoensis Ashm. (MS)—all s. 
IPTERA— Mycetophilide : (10) Dynatosoma thoracica Coq.(MS); Empide: 
(11) Rhamphomyia piligeronis Coq. (MS); Syrphid@: (12) Chilosia capillata 
Lw.; (13) Melanostoma obscurum Say; (14) Rhingia nasica Say ; Anthomy- 
ide: (15) Hylemyia plumosa Coq. (MS); (16) Mydza flavipes Coq. (MS); 
Oscinide : (17) Chlorops trivialis Lw.— all s. 
COLEOPTERA--Mordellide : (18) Mordellistena biplagiata Hel.; Curcu/ion- 
ide : (19) Idiostethus subcalvus Casey, both s. 
PTELEA TRIFOLIATA L.— According to Hildebrand (1) and 
Kerner (3), the flowers are staminate and perfect. Urban (2) 
indicates that Prelea is dicecious, and that self-pollination is 
impossible. As far as I have observed, it has appeared that this 
Species is dicecious. | could find no perfect flowers. 
The greenish white blossoms expand from 10 to 15™" and 
are crowded in compound cymes, which are nearly level topped 
and form convenient resting places for insects. In both forms 
nectar is secreted by the gynophore and is slightly concealed by 
the hairy bases of the filaments. 
The following table shows the kinds of insects taken on Xan- 
thoxylum Americanum and Prelea trifoliata, the former blooming 
= April 12th to 28th and the latter from May 8th to June 
2th: 
Xanthoxylum hoses Other Hymenoptera Apidz Andrenidz Diptera Lepidoptera 
: canum (39) 0 19 3 $ 
Prelea trifoliata (51) I2 I 22 14 2 
The difference in Apide may be partly on account of the 
mer having the nectar more concealed, but is mainly, I think, 
on account of the blooming time. At any rate, three of the 
Apide taken on Xanthoxylum have finished their flight before 
for 
