16 ANGIOSPERMAE DICOTYLEDON ES 



few. On the island of Fohr I observed small flies (Muscidae) visiting the flowers, 

 and of course these might effect self- or cross-pollination with equal facility. 



Willis and Burkill ('Fls. and Insects in Gt. Britain./ I, p. 267) also found 

 flowers in central Wales of only 5 mm. in diameter. They did not observe any 

 secretion of nectar, and saw no insect visitors. The anthers dehisce when the flower 

 opens, and get covered all over with pollen, which they also shed on the stigmas. 

 The stamens move outwards after dehiscence of the anthers. Self-pollination is 

 completely effective. When flowering is over, the peduncle bends downwards during 

 the ripening of the fruit. 



35. B. aquatile Wimm. (=Ranunculus aquatilis Z., in part). (Axell, ' Om 

 anord. for fanerog. Vaxt. befrukt.,' p. 14 ; Hildebrand, 'Die Geschlechtsvert. b. d. 

 Pfl./ p. 17 ; Herm. Midler, ' Fertilisation,' p. 74 ; ' Weit. Beob.,' I, pp. 318-19; Beyer, 

 1 D. spont. Bewegungen d. Staubgefasse u. Stempel '; Crid, C. R. Acad, sci., Paris, ci, 

 1886, p. 1025 ; Kirchner, ' Flora v. Stuttgart,' pp. 263-4 ; Knuth, ' Bl. u. Insekt. a. d. 

 nordfr. Ins./ pp. 18, 147.) The faintly odorous flowers are homogamous or (on the 

 island of Fohr) slightly protogynous. They spread out their petals in the sunshine, 

 forming a yellow-centred white star 20-25 mm. in diameter, but the size varies (and 

 with it the number of stamens) to such an extent that, according to Kirchner, it may 

 be as low as 3-4 mm. (and the number of stamens may be reduced from over 20 

 to 8). Many insects may, however, be attracted, for the plants are usually associated in 

 large numbers, and not infrequently shallow ditches and ponds are completely filled 

 with them, so that the surface is covered with white blossoms. After the flower has 

 opened, the anthers at once dehisce, covering themselves with pollen. The stigmas 

 usually mature either simultaneously with the stamens or slightly earlier. In the 

 latter case, cross-pollination must result from the visits of insects, if these come 

 from a flower with dehisced anthers. When homogamy obtains, insects may effect 

 either cross- or self-pollination, for they sometimes alight on the centre, sometimes 

 on the margin of the flower, and then creep about. If insect-visits fail, automatic 

 self-pollination takes place, for pollen can readily fall from the anthers on the 

 adjacent stigmas. 



When the flowers are submerged in consequence of flooding, they remain closed 

 and pollinate themselves (Axell, Hildebrand). 



According to Warnstorf (Verh. bot. Ver., Berlin, xxxviii, 1896), the flowers 

 are homogamous and autogamous in the neighbourhood of Ruppin. The pollen is 

 yellow, irregularly ellipsoidal, and tuberculated. The grains are about 25 p 

 broad and 37 fi long. 



Visitors. The following have been observed by Hermann Miiller (H. M.) 

 and myself (Kn.). A. Coleoptera. (a) Byrrhidae: 1. Pedilophorus aeneus F., 

 with its head in the nectaries (H. M.). \b) Chrysomelidae: 2. Agelastica alni Z., 

 resting idly on the flowers (H. M.) ; 3. Helodes phellandrii Z., devouring anthers 

 and flower-leaves (H. M.). (c) Elateridae : 4. Limonius cylindricus Payk., its head 

 and thorax yellow with pollen. B. Diptera. (a) Bibionidae : 5. Dilophus vulgaris 

 Mg. J and 5, freq. (H. M.). (i) Empidae : 6. Empis rustica Fall. (H. M.) ; 7. Hilara 

 maura F. (H. M.). (c) Muscidae: 8. Anthomyia sp., skg. and po-cltg. (Kn., Fohr; 

 H. M.); 9. Cyrtoneura hortorum Fall. S (H. M.) ; 10. Hydrellia griseola Fall, skg. 

 and po-cltg., extremely abundant (H. M.); 11. Hylemyia sp. (H. M.); 12. Onesia 

 floralis R.-D. $, freq. (H.M.) ; 13. O. sepulcralis Mag., freq. (H. M.) ; 14. Sarcc- 



