RUT ACE AE 239 



XXVI. ORDER RUTACEAE JUSS. 

 1. Tribe Ruteae. 



Literature. Knuth, Grundriss d. Bliitenbiologie, p. 39; Urban, Jahrb. bot. 

 Gart., Berlin, ii, 1883, pp. 366-404. 



The species of the genus Ruta bear nauseous flowers, which, by their penetrating 

 odour and dull yellow colour, attract Hymenoptera, and particularly Diptera that are 

 fond of putrid matter. On the other hand, the species of Dictamnus are visited 

 by Apidae. Owing to their marked protandry, cross-pollination results in the species 

 of both genera from insect-visits. 



177. Ruta Tourn. 



Flowers with exposed nectar, secreted by a fleshy disk beneath the ovary. 



604. R. graveolens L. (Sprengel, 'Entd. Geh.,' p. 236; Herm. Muller, 

 'Fertilisation,' pp. 160-2, ' Weir.. Beob.,' II, p. 213 ; Schulz, ' Beitr'age,' II, pp. 59, 60; 

 Kirchner, ' Flora v. Stuttgart,' p. 348 ; Knuth, ' Blutenbiol. Herbstbeob.') As 

 Hermann Muller justly remarks, the flower-mechanism of this species is very like 

 that of Parnassia palustris, for the stamens first of all ripen successively, and then 

 the stigma matures. The transfer of pollen is secured in both by the fact that 

 the middle of the flower, which offers the most convenient alighting-place, is occupied 

 first by a dehisced anther, and afterwards by the stigma. Finally, in both, the 

 exposed nectar attracts similar guests (flies and short-tongued Hymenoptera), but 

 while the white flowers of Parnassia are also visited by beetles, the dull yellow 

 flowers of Ruta are not. 



There is, however, this difference. In Ruta, according to Urban, all the 

 stamens once more curve upwards before the stigma withers, so that should the anthers 

 retain any pollen this falls upon the stigma, and thus renders automatic self-pollina- 

 tion possible towards the end of anthesis. Schulz, however, states that autogamy 

 is impossible. 



Visitors. Hermann Muller (H. M.) in Westphalia, Buddeberg (Budd.) in 

 Nassau, and myself (Kn.) in Schleswig-Holstein, have observed the following. 



A. Diptera. (a) Musa'dae: 1. Anthomyia obelisca Mg., skg. and po-dvg. 

 (Winnert2); 2. A. pratensis Mg., do. (Winnertz); 3. A. radicum Z., do. (Winnertz); 

 4. Calliphora erythrocephala Mg., do. (Kn., H. M.) ; 5. Lucilia caesar Z., do. (Kn.) ; 

 6. L. cornicina F., do. (H. M.) ; 7. L. sylvarum Mg., do. (H. M.) ; 8. Pollenia rudis 

 F., do. (H. M.) ; 9. Sarcophaga albiceps Mg., do. (H. M.); 10. S. carnaria Z., do. 

 (H. M., Kn.); n. S. haemorrhoa Mg., do. (H. M.) ; 12. Scatophaga stercoraria Z., 

 do. (Kn.); 13. Sepsis sp., do. (H. M.). (b) Stratiomyidae : 14. Chrysomyia formosa 

 Scop., skg. (Budd.); 15. Sargus cuprarius Z., skg. and po-dvg. (H. M.). (c) Syrphidae : 

 16. Ascia podagrica F., skg. and po-dvg. (H. M.); 17. Eristalis sepulcralis Z., do. 

 (H. M.); 18. E. tenax Z., do. (Kn.); 19. Helophilus floreus Z., do. (H. M.); 20. 

 Melithreptus pictus Mg., do. (H.M.); 21. Syritta pipiens Z., do. (H. M., Kn.); 

 22. Syrphus nitidicollis Mg., do. (H. M.) ; 23. S. ribesii Z., do. (H. M.). B. Hymeno- 

 ptera. (a) Apidae: 24. Apis mellifica Z. $, skg. (H. M., Kn.); 25. Halictus 

 sexnotatus K. 5, do. (H. M.) ; 26. H. tetrazonius Kl. $, do. (H. M., Kn.); 27. Pro- 

 sopis sinuata Schench 5, do. (H. M., Budd.) ; 28. Sphecodes gibbus Z. >, do. (Budd.). 



