572 



ANCIOSPERMAE—DICOTYLEDONES 



corymbose inflorescences, these are very conspicuous, especially as the greatly 

 protruding stylar branches are white, while the margins of the involucral bracts 

 are reddish in colour. The corolla-tube is 2^ mm. long, ending in a bell 

 scarcely 2 mm. in length, from which the stylar branches project for about 5 mm. 



In the first stage of anthesis the lowest part of the stylar branches (beset with 

 stigmatic papillae) remains in the corolla -tube, while their upper three -fourths 

 (covered with sweeping- hairs) project freely, and diverge so widely that insect 

 visitors touch them, and rub off the pollen-grains clinging to the sweeping-hairs. 

 In the second stage of anthesis the lower parts of the stylar branches project 

 from the bell, so that insects probing for nectar must come into contact with 

 the stigmatic papillae. Wamstorf adds that the anther-cylinders do not project 

 out of the florets, and that the sweeping -hairs are thick, bluntly conical papillae, 

 sometimes two-celled, delicately striated, and projecting horizontally. The pollen- 

 grains are white, roundish to ellipsoidal, 

 spinose, on an average 25 /x in diameter. 

 If insect visitors are sufficiently 

 numerous to remove the pollen from 

 the sweeping- hairs before the stigmas 

 project, cross-pollination is assured. If, 

 however, pollen still clings to the sweep- 

 ing-hairs when the lower parts of the 

 stylar branches protrude, self-pollination 

 is equally possible as the result of insect- 

 visits. Automatic self-pollination cannot 

 lake place in the total absence of 

 visitors, but geitonogamy undoubtedly 

 may, for the stylar branches spread 

 out so far that they occasionally touch 

 the stigmas of adjacent florets. Kerner 

 ('Nat. Hist. PI.,' Eng. Ed. i, II, p. 319) 

 calls particular attention to this possibility 

 (Fig. 191). 



Visitors. — Of these Lepidoptera 

 are the chief observed. 



Herm. Miiller (Alps) noticed 6 

 Diptera, 4 Hymenoptera, and 6 Lepi- 

 doptera. He (H. M.) and Buddeberg 

 (Budd.) give the following list for Central 

 Germany. — 



A. Diptera. (a) Muscidae: i. Dexia canina i^. (H. M.); 2. Echinomyia fera 

 L. (H. M.) ; 3. Lucilia albicepsil^. (H. M.). {U) Syrphidae: 4. Eristalis arbustorum 

 L. freq., po-dvg. (H. M.); 5. E. nemorum Z., do. (H. M.); 6. E. tenax Z., do. 

 (H. M.). B. Hymenoptera. Apidae: 7. Apis mellifica Z. 5, skg. (H. M.); 



8. Psithyrus vestalis Fourcr. $, skg. (H. M.). C. Lepidoptera, (a) Bcmbycidae: 



9. Calhmorpha dominula Z., skg. (Budd.). (V) Rhopalocera: all skg. : 10. Argynnis 

 paphia Z., freq. (H. M., Budd.); 11. Erebia medusa S.V. (H. M.); 12. Hesperia 



Fig. 191. GeitouogaTny of Eupatorium can- 

 nabinum, L. (after Kemer). Fertilization of neigh- 

 iKittring florets is effected by means of pollen adhering 

 to the stylar branches. 



