ROSACEAE 345 



not quite erect, automatic self-pollination can easily take place during the second 

 stage, should insect-visits fail, the pollen falling from the outer longer stamens upon 

 the stigma. 



Visitors. — 1 saw the following at Kiel. — 



A. Diptera. Syrphidae : i . l-^ristalis tenax /.. B. Hymenoptera. Apiilac : 



2. Apis mellifica L. 5, skg. ; 3. Bombus teirester L. 5, do. C. Lepidoptera. 

 Rhopaloccra : 4. Pieris sp., skg. 



Herm. Miiller gives the following list for Prunus domestica, P. avium, and 

 P. cerasus (' Fertilisation,' p. 222). — 



A. Diptera. Syrphidae: i. Eristalis arbustorum /,., skg.; 2. E. tenax Z. ; 



3. Riiingia rostrata L., freq., skg. B. Hymenoptera. Apidae: 4. Andrena 

 albicans Miill. 5 and S, very freq., po-cltg. and skg. ; 5. A. fulva Schr. j, skg. and 

 po-cltg.; 6. Apis mellifica L. 5, very common, skg.; 7. Bombus hortorum 7,. 5, do.; 

 8. B. lapidarius L. 5, do.; 9. B. terrester L. 5, do.; 10. Osmia cornula Ltr. 5 and 

 $, do. ; II. O. rufa L. 5 and S, freq., do. C. Lepidoptera. Rhopahcera: 12. 

 Pieris brassicae L., skg. ; 13. P. napi L., do. ; 14. P. rapae L., do. 



MacLeod observed Apis in Flanders (Bot. Jaarb. Dodonaea, Ghent, vi, 1894, 

 P- 325)- 



822. P. cerasifera Ehrh. (Knuth, ' Bloemenbiol. Bijdragen.') — Focke says that 

 this species is somewhat infertile when isolated. 



Visitors. — I observed Andrena albicans Miill. 5, skg. 



823. P. insititia L. — Kirchner {' Beitriige,' p. 35) says that the flower mechan- 

 ism of this species agrees with that of P. domestica, but cross-pollination is more 

 likely to occur, for the style sometimes exceeds the longest stamen in length. 



Visitors.— In the Kiel Botanic Garden I only observed .\ndrena albicans ISlUll. 

 $, skg. 



824. P. avium L. — For this species Kirchner (' Beitrage,' pp. 32-4) gives the 

 following account, supplementing the observations of C. K. Sprengel and Herm. 

 Miiller ('Fertilisation,' p. 222). The pure white flowers are faintly fragrant. The 

 corolla does not usually flatten itself out, but forms an almost hemispherical bell, 

 about 10-12 mm. deep, and 17-25 (on an average 22) mm. in diameter. The flower 

 is generally pendulous, and therefore faces downwards. Owing to the shape and 

 arrangement described the stamens and pistil of the sweet cherry are much better 

 protected against rain than is the case in other fruit trees. The length of anthesis 

 is 7-8 days. The flowers are homogamous, but automatic self-pollination cannot 

 normally take place. The stamens are of different lengths : those nearest the centre 

 being only 2-3 mm. long, while the outermost ones are 9-1 1 mm. 



The stigma is mature when the flower opens ; it stands at about the same level 

 as the longest stamens. The stamens are divergent and, excejit in the case of a few 

 of the short (inner) ones, their anthers are still unripe. The pollen of those which 

 have dehisced can scarcely reach the stigma. Dehiscence progresses centrifugally in 

 a not "itry regular fashion, so that on the second day of anthesis a number of the 

 outer anthers are still closed, but these dehisce extrorsely in the course of the day. 

 The style projects in the middle of the flower beyond the obliquely diverging 

 stamens. These relative positions are maintained till the flower fades, so that 

 automatic self-pollination is infrequent, and can only occur accidentally. Insects 



