38o ANGIOSPERMAE—DICOTYLEDONES 



secrete abundant nectar ; they are consequently much sought by numerous insects, 

 particularly bees, which bring about cross-pollination and also lead to the formation 

 of the numerous hybrids. 



Kerner states that the 5 flowers of many species (e. g. S. fragilis L., S. viminalis 

 L., S. triandra Z., and S. purpurea L.) mature earlier than the S flowers of adjacent 

 trees. Jordan says that the anthers turn their pollen-covered surfaces towards the side 

 in such a way that the proboscis of an insect inserted between the stamens to suck 

 nectar must be thickly dusted with pollen. Heinricher, von Seemen, and others 

 observed androgynous inflorescences. 



One of three androgynous inflorescences of S. Caprea L. examined by Heinricher 

 bore mixed S and § flowers at the base, and only $ on the upper half; the second 

 bore only 5 at the base, only S at the top, and both S and 5 in the middle ; the 

 third bore only 5 flowers. 



As insect visitors go from one species of willow to another indiscriminately, it is 

 difficult to assign them to individual species. In the following lists, therefore, the 

 visitors of various species are often grouped together, as was done by Hermann 

 MuUer. 



2576. S. cinerea L. ; 2577. S. Caprea L. ; 2578. S. aurita L., and others. 

 (Herm. Miiller, 'Fertilisation,' pp. 524-5, ' Weit. Beob.,' II, pp. 210-11; Knuth, 

 ' Bloemenbiol. Bijdragen.') — 



Visitors. — Burkill observed the following on the Yorkshire coast (' Fertilisation 

 of Spring Flowers '). — 



A. Diptera. {a) Muscidae : i. Scatophaga stercoraria Z., on $ and $ catkins, 

 skg. (i) Straiiomyidae: 2. Lasiopa sp., as i. po-cltg. (c) Syrphidae: 3. Eristalis 

 arbustorum Z., on S catkins ; 4. Melanostoma quadrimaculata Verral, on 5 catkins, 

 skg. B. Hymenoptera. Apidae : 5. Andrena gwynana J^., on S catkins, skg. 

 and po-cltar. ; 6. Apis mellifica Z., on J and 5 catkins, very common, skg. ; 7. Bombus 

 agrorum Z"., on J catkins, skg. ; 8. B. terrester Z., on 5 and 5 catkins, skg. 



Krieger observed the following bees on S. Caprea at Leipzig. — 



Apidae : 1. Andrena albicans A/ii//. ; 2. A. cineraria Z. a S ; 3. A. eximia Sm.; 

 4. A. extricata Sm.; 5. A. flavipes /"c. ; 6. A. gwynana Jy.; 7. A. nitida Zoarrr. ; 

 8. A. ovina Klug.; 9. A. parvula A'.; 10. A. tibialis K.; 11. Bombus derhamellus 

 K. 5 (=B. rajellus ZT.); 12. B. hortorum Z. 5; 13. B. terrester Z.; 14. Colletes 

 cunicularius Z. ; 15. Halictus calceatus Scop. (=H. cylindricus F.); 16. H. levis 

 Ths.^; 17. H. nitidiusculus A''. ; 18. Nomada lineola Pz. ; 19. Osmia rufa Z.J; 

 20. Podalirius acervorum Z. $, freq. ; 21. Psithyrus quadricolor Lep. a 5. 



Herm. Miiller gives the following list for the 3 species. — 



A. Coleoptera. {a) Elaieridae: i. Corymbites castaneus Z. ; 2. Limonius 

 parvulus Pz. {I) ISJitidulidae : 3. Meligethes sp., freq., nect-lkg. B. Diptera. 

 \a) Bibionidae : 4. Bibio johannis Z., skg. ; 5. B. marci Z., do. ; 6. Dilophus vulgaris 

 j^/g; freq. {i) Bombyliidae : 7. Bombylius major Z., skg. (c) Conopidae: 8. Myopa 

 buccata Z., not infreq., skg. ; 9. M. testacea Z., do. ; 10. Sicus ferrugineus Z., do. 

 (jT) Empidae : 11. Empis sp., freq,, skg.; 12. Rhamphomyia sulcata Fall., skg. 

 [e) Muscidae: 13. Calliphora erythrocephala yli'^., skg. ; 14. Exorista sp. ; 15. Gonia 

 ornata Mg., skg.; 16. Pollenia rudis F., po-dvg. ; 17. P. vespillo F., skg. and 

 po-dvg. ; 18. Scatophaga merdaria Z., freq., skg.; 19. S. stercoraria Z., do. 

 (y") Syrphidae: 20. Brachypalpus valgus Pz., skg. and po-dvg.; 21. Cheilosia 

 brachysoma Egg., do.; 22. C. chloris Mg., do.; 23. C. modesta Egg., do.; 



