194 



ANGIOSPERMAE—DICOTYLEDONES 



only as long as the sepals, and their stamens possess yellow degenerate anthers. 

 Warnstorf usually found only hermaphrodite flowers at Ruppin, 1-4 stamens being 

 vestigial in rare instances. The five outer stamens bend over the stigmatic branches, 

 and discharge their pollen when these are still closely apposed. Meanwhile the 

 inner stamens — with anthers as yet immature — lie remote from the centre between 

 the petals, and only dehisce when the stigmatic branches begin to spread out. 

 After dehiscence the inner stamens curve back again, so that all the anthers are in 

 a peripheral circle when the stigmatic branches have fully diverged. Self-pollination 

 is thus rendered very difficult. The pollen clings to the anthers for a time. The 

 pollen-grains are white, dodecahedral and smooth, with an average diameter of 37-43 ^. 



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

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



A. Coleoptera. NitiduUdae : i. Meligethes, freq., nect-lkg. (H. M.). B. 

 Diptera. (a) Muscidae: 2. Anthomyia, skg. (H. M.). {b) Syrphidae: 3. Ascia 

 podagrica F., freq., skg. (H. M.) ; 4. Eristalis arbustorum Z., skg. and po-dvg. (H.M., 

 Kn.) ; 5. Helophilus lineatus F., freq., skg. (H. M.) ; 6. Rhingia rostrata Z., skg. and 

 po-dvg. (Kn.); 7. Syritta pipiens Z., ditto (H. M., Kn.) ; 8. Syrphus sp., ditto (Kn.). 

 C. Hymenoptera. Apidae: 9. CoUetes daviesanus A', j , skg. (Budd.) ; 10. Halictus 

 quadricinctus Z'. 5 , skg. (H. M.); 11. H. sexnotatus K. 5, skg. (H. M.); 12. Prosopis 

 communis Nyl. j, skg. (H. M.); 13. P. hyalinata Sm. 5, skg. (H. M.). D. Thysano- 

 ptera. 14. Thrips, very freq. (H. M.). 



MacLeod saw a short-tongued bee in Flanders (Bot. Jaarb. Dodonaea, Ghent, 

 vi, 1894, p. 378), as well as 3 hover-flies and 3 other Diptera (op. cit., vi, 1894, p. 170). 



139. Cerastium L. 



Flowers mostly white and protandrous, with half-concealed nectar secreted 

 as in the preceding genera. 



483. C. arvense L. (Herm. MuUer, 'Fertilisation,' pp. 131-2, ' Weit. Beob.,' 



II, p. 229; Schulz, ' Beitrage,' I, p. 24; Kirchner, 'Flora v. Stuttgart,' p. 240; 



Knuth, ' Bloemenbiol. Bijdragen ' ; 

 Loew, ' Bliitenbiol. Floristik,' pp. 

 389, 397; Warnstorf, Verh. bot.Ver., 

 Berlin, xxxviii, 1896.) — The flowers 

 of this species are protandrous, and, 

 according to Hermann Miiller, agree 

 with Stellaria Holostea as regards 

 the position of the nectaries, and the 

 order of maturation of stamens and 

 stigmas. There is, therefore, an 

 agreement as to the probability of 

 cross-pollination by insect-visits, and 

 the possibility of self-pollination 

 when such visits fail. The plants 



examined by Warming in Greenland, as far north as 67° N. lat., had somewhat 



smaller protandrous flowers. 



Besides the hermaphrodite flowers, smaller female ones with degenerate whitish 



stamens have been observed. Schulz states that their distribution is usually 



Fig. 57. Cerastium arvense, L. (after Herm. Miiller). 

 (I) Flower in the first part of the first (male) stage: the 

 anthers of the outer stamens are covered with pollen, those of 

 the inner ones are stilt closed, and the stigmatic branches 

 are still curved inwards. (2) Flower in the altnost exclusively 

 female stage ; the anthers of the outer stamens have partly 

 fallen off, partly shrivelled ; those of the inner whorl are still 

 sparingly covered with pollen ; the stigmas are mature. 



