part u1.] THE MECHANISMS OF FLOWERS. 511 
(16) Athalia spinarum, F.,s. B. Diptera—(a) Syrphide: (17) Eristalis tenax, 
L. ; (18) E. pertinax, Scop. ; (19) E. nemorum, L. ; (20) E. arbustorun, L. ; 
(21) E. sepulcralis, L. ; (22) E. intricarius, L. ; all ab., s. or fp. ; (23) Helo- 
philus floreus, L. ; (24) Syritta pipiens, L. ; (25) Chrysotoxum festivum, L. ; 
(26) Melithreptus scriptus, L. ; (27) M. teniatus, Mgn. ; (28) Syrphus py- 
rastri, L. ; (29) Pipiza funebris, Mgn. ; (30) Cheilosia scutellata, Fallen ; (6) 
Muscide : aH) Pollenia Vespillo, F. ; (82) Musca corvina, F. ; (33) Lucilia 
cornicina, F. ; (34) Sarcophaga carnaria, L. ; (c) Stratiomyide : (35) Odon- 
tomia viridula, F. ; (36) Stratiomys Chameleon, Deg., ab. ; (37) Str. riparia, 
Mgn. ; most of these flies sucking, the Syrphidee also eating pollen. C. Lepido- 
ptera—(38) Vanessa urtice, L.; (39) Pieris brassice, L. ; (40) P. napi, L. ; 
(41) Polyommatus Phlceas, L., all s. 
370. Potyconum Bistorta, L.—As in P. jfagopyrum, the 
flowers are made conspicuous by aggregation and by their coloured 
Fic. 178.—Polygonum Bistorta, L. 
1.—Flower, in first (male) stage. 
2.—Ditto, in second (female) stage. 
perianth; eight red swellings at the base of the stamens. secrete 
honey, which lies freely open at the bottom of the flower. The 
power of self-fertilisation has been lost; but while in P. fagopyrum 
crossing has been insured by the development of long-styled and 
short-styled stocks, in P. Bistorta the same end has been gained by 
complete proterandrous dichogamy. In the first stage, the anthers 
protrude freely from the flower, which never expands very widely ; 
afterwards, when the anthers are withered and mostly fallen off, 
the ends of the styles with their stigmas protrude. | 
On the meadows at Brilon, I saw the flowers plentifully visited 
by flies, but I was busy with other observations and can name 
only the following easily recognised forms: Rhingia rostrata, L., 
