30 Bulletin Wisconsin Natural History Society. [Vol. 7, No's. 1-2. 



its neighbor, and giving rise to a mode of cross-pollination called 

 geitonogamy by Kerner 14 . The same conditions prevail in our 

 3 species of Eupatorium which are considered in the second part 

 of this paper. 



Referring to Aster Kerner 13 states, that geitonogamy takes 

 place between ray florets, and disk florets occupying the outer 

 row of the disk. In our species of Aster the disk flowers are sit- 

 uated so far above the ray flowers that a meeting of the stylar 

 branches of two of these neighboring flowers is entirely out of the 

 question. From a repeated examination of the flowers of several 

 species of Aster besides those treated in this paper I feel con- 

 vinced, that in the asters of our region geitonogamy does not 

 occur in the manner indicated. Kerner 1 " also mentions the fact 

 that in Aster automatic self-pollination may be brought about in a 

 discal floret when its stylar branches cross each other, and pollen 

 adhering to one of these branches is deposited on the stigmatic 

 papillae of the other branch. Knuth 17 has never observed such a 

 crossing of the stylar branches in Aster. In our species of Aster 

 under discussion two groups can be recognized, one comprising 

 A. laterfflorus, A. paniculatus, A. furcatus, and A. macrophyllus 

 in which such a crossing occurs, and the other group, consisting 

 of A. prenantlwides, A. Drummondii, A. pnniceus, A. Imvis, and 

 A. novce-anglice without any such movements of the stylar 

 branches. In these latter species the stylar branches at first be- 

 come separated to a slight extent, remaining in contact with their 

 apices onby, but in the older flower divergence becomes more pro- 

 nounced and the tips also move away from each other. With the 

 first named species in which the stylar branches effect a crossing 

 the case is entirely different. At the bes'inninsr divergence sets 

 in to the same extent as in the other group, but after 2 or 3 days 

 a movement in the opposite direction (convergence) begins and 

 the stylar branches are carried past each other, whereby they re- 

 main in close contact with their corresponding lateral portions. It 

 is interesting to note that those species in which automatic self- 

 pollination may result from the crossing of the stylar branches 

 have shorter tubes than those of the second group. In the first the 

 tube length ( length of the upper distended portion of the tube) 

 ranges from 1 to i l / 2 mm., in the others from 1^4 to 4 mm. 



A. Kerner v. Marilaun. Pflanzenleben. 2nd ed., 1S96. Vol. II, p. 274. 



15) Loc. cit., Vol. II., p. 294. 



16) Loc. cit.. Vol. II., p. 223. 



17) P. Knuth. Handbuch d. Bluetenbiolosie, Vol. II., p. 580. 

 Handbook of flower pollination, Vol. II., p. 581. 



