5i8 ANGIOSPERMAE—DICOTYLEDONES 



pollination. Hermann Miiller and Kirchner, on the contrary, found them to be 

 homogamous. The insect visitors of these flowers, however, effect cross-pollination, 

 for they alight upon the central stigma, and do not touch the radiating stamens till 

 afterwards. Hermann IMiiller and Kirchner add that nectar is secreted so abundantly 

 that, if not removed by insects, it covers the nectary with a white sugary crust after 

 the flower has faded. Wittrock calls attention to the fact that the ivy but rarely 

 blooms in Central Sweden, the most northerly point for this being in Sodermanland 

 {58° 57' N. lat.). The same writer mentions that the ivy flowering every October in 

 a Stockholm greenhouse never produces fruit, probably owing to the absence of the 

 insects necessary for pollination. Automatic self-pollination would therefore seem to 

 be ineffective. 



Visitors. — Burkill and Willis observed the following near Cambridge (' Fls . 

 and Insects in Gt. Britain.'). — 



A. Diptera. {a) Muscidae : I. Anthomyia. 2 sp. ; 2. Aricia lucorum /^a//. ; 

 3. Calliphora erythrocephala il:^., very common, skg. ; 4. Chloropisca ornata j^. ; 

 5. Hydrellia griseola Fall. ; 6. Limnophora sp. ; 7. Lucilia sp., skg. ; 8. Onesia 

 sepulcralis Mg., skg.; 9. Phytomyza sp. ; 10. Aricia lardavia F.; ii. Pollenia 

 rudis i^., freq., skg. ; 12. Drosophila graminum i^:^//. ; 13. Scatophaga stercoraria Z., 

 skg.; 14. Siphona geniculata Z)f^., do. ; 15. Trichophthicus cunctans /I^. (b) Syr- 

 phidae: i6. Eristahs tenax L., freq., skg. [c) Mycetophilidae: 17. Bolitophila fusca 

 Mg.\ 18. Metriocnemus sp.; 19. Onhocladius sp. ; 20. Sciara sp. B. Hymeno- 

 ptera. {a) Ichneiimonidae : 21. Five undetermined species. {l>) Vespidac : 22. 

 Vespa vulgaris L., freq., skg. C. Lepidoptera. Torlricidae : Tortrix sp. 



The following were recorded by the observers, and for the localities stated. — ■ 



Knuth, the wasp Vespa vulgaris L., the Muscid Aricia lardaria F., and the 

 earwig Forficula auricularia. Herm. Miiller, 3 Muscids — i. Calliphora erythroce- 

 phala Mg. ; 2. Echinomyia fera L., freq.; 3. Lucilia cornicina F, do. Plateau 

 (Belgium), the wasp Vespa germanica Z., in countless numbers ; 2 hover-flies (Eris- 

 talis, Helophilus); and a Muscid (Calliphora vomitoria £., freq.). Schletterer (Pola), 

 the Scoliid Scolia hirta Sc/n-. (Oct. 10), and (also in October) 3 true wasps — 

 I. Eumenes mediterranea A';r/;//. ; 2. Polistes gallica /,. ; 3. Vespa germanica Z". 



L. ORDER CORNACEAE DC. 

 382. Comus L. 



Flowers homogamous ; with exposed nectar, secreted by a ring surrounding the 

 style. 



1203. C. sanguinea L. (Herm. Miiller, 'Fertilisation,' pp. 287-8, ' Weit. 

 Beob.,' I, p. 301; Kirchner, 'Flora v. Stuttgart,' p. 399; Knuth, ' Bloemenbiol. 

 Bijdragen,' ' Bliitenbiol. Beob. a. d. Ins. Riigen.') — Hermann Miiller says that in this 

 species the stamens and stigmas develop simultaneously. The anthers are introrse, 

 and at the same level as the stigma, though some distance from it. The larger 

 insects that alight on the inflorescence, or on a single flower, will therefore, when 

 licking the nectary, usually touch an anther or two with one side of their heads, and 

 the stigma with the other. Should they creep further on the same inflorescence, or 

 visit another, cross-pollination will be favoured. Smaller flies and beetles, on the 

 contrary, owing to their erratic movements, will sometimes effect cross- sometimes 



