Robertson — Flowers and Insects. 441 
Sarcophagidae: (16) Sarcophaga sp., s., freq.; Muscidae: (17) Lucilia 
sylvarum Mg.,, s. 
POTENTILLA CANADENSIS L.— Except in their yellow color 
and smaller size, the flowers bear a strong resemblance to 
those of Fragaria. The plants are common and are often 
collected in patches of considerable size. A few stems rise 
from the same base and are ascending or trailing. A single 
plant does not bear many open flowers at a time, since the 
flowers are single on axillary peduncles, and there is there- 
fore an increased opportunity for cross-pollination between 
distinct plants. 
- The flowers expand horizontally about fifteen millimetres, 
Nectar is secreted on the narrow line between the outer pistils 
and the stamens. The pistils have their stigmas receptive 
before the anthers dehisce. In case cross-pollination does 
not take place oefore the pollen is discharged, self-pollination 
may occur by insect aid, or spontaneously by the pollen fall- 
ing upon the stigmas. 
The blooming time is from April 30 to June 17. The 
Visitors mentioned below were taken on May 18 and June 2:— 
Hymenoptera—Apidae: (1) Bombus americanorum F. 9, s.; (2) Ceratina 
dupla Say 99, s., freq.; (3) C. tejonensis Cr. 9’, s.; (4) Alcidamea prod- 
ucta Cr. ¥', s.; (5) Osmia albiventris Cr. 9, s., (6) Stelis lateralis Cr. ¢', 
S.; (7) Nomada annulata Cr. 4, 8.; (8) N. sayi Rob. ¢', s.; Andrenidae: (9) 
Andrena ziziae Rob. ¢'Q, s., ab.; (10) H. pectoralis Sm. 9, s.; (11) H. lig- 
atus Say 9, s.; (12) H. fasciatus at 2, s.; (18) H. confusus Sm. Q, 8.; 
(14) Augochlora pura Say 9, s. and plats .3 (15) A. similis Rob. 9, s.; 
se (16) Sphecodes aeaenauiiia nave 2 s.; (17) Prosopis affinis Sm. @’, 
alenenicee: (18-20) Odynerus spp., s., freq.; (21) O. anormis Say, s. 
" Diptera —Spepadiao: (22) Paragus ie Fil. ; (23) Syritta pipiens L., Le: 
Tachinidae: (24) sp., s.; (25) Cistogaster occidua WIk., s.; Sarcop 
ae onic sr ., 8.3 Muscidae: (27) Lucilia sp., 8.; Anthomyidae: ellis 
Chortophila 
Laphdecbers<Neeaehrtdtn (29) Phyciodes tharos Dru., s. 
Rosa _Humitis Marsh.— The flowers expand several centi- 
metres. The stamens are turned outwards so strongly that 
insects landing near the center of the flower are likely to touch 
the stigmas before becoming dusted with pollen from the same 
ower. Nectar is wanting. The principal visitors are bumble- 
bees and other large bees, which collect the pollen, and 
