40 Bulletin Wisconsin Natural History Society. [Vol. 7, Nos. 1-2. 



ODOR. 



In the flowers just mentioned there is undoubtedly a connec- 

 tion between the effect of the odor, and the great number of in- 

 sects, of species as well as of individuals that pay their attention 

 to these flowers. In Arctium Lappa, for example, conspicuousness 

 can hardly be taken into consideration ; there is on the contrary an 

 extremely modest display of color (purple) in the inflorescence, 

 but a distinct fragrant odor is perceptible, and the flowers, especi- 

 ally when these plants are gathered in groups are well visited. In 

 our 2 species of Bupaforium, in which the white capitula are ar- 

 ranged in a flat-topped inflorescence there is quite a difference in 

 the number of insects at the flowers. Bupaforium perfoliatum has 

 sweet-scented flowers that are very attractive, and 113 species, 

 many of them represented by numerous individuals, were noticed 

 as visitors. In Maine Lovell 21 , has observed more butterflies on 

 this species than on any other Composite of his region. In Bupa- 

 torium urticcefolium on the other hand with a very faint odor I 

 succeeded in obtaining 58 species of visitors only, and there is not 

 such an assemblage of individuals at the flowers as in the preceding 

 species. Of course the greater length of the tube in this species 

 (2 mm., only 1 mm. in B. perfoliatum) has something to do with 

 the smaller number of visitors, but quite a number of our species 

 with longer tubes are more extensively visited. The examples 

 cited so far refer to flowers emitting a sweet odor. In some of 

 our species of Composite the flowers produce a more or less dis- 

 agreeable, or even fetid odor, and this seems to attract a smaller 

 number of insects than a fragrant odor. Of the yellow flowers of 

 Tanecetum vulgar e Knutlr 2 , states that they are visited by a large 

 number of insects, but H. Mueller's 23 list contains 27 visitors only. 

 In the vicinity of Milwaukee they are poorly visited, and in spite 

 of repeated observations I have not been able to bring the number 

 of the list above 34. This number seems insignificant as compared 

 with the 141 visitors of the goldenrod Solidago canadensis, and 

 the 182 visitors of another goldenrod Solidago juncea, the tubal 

 florets of which correspond in color and dimensions to those of 

 Tanecetum. Anthemis Cotnla furnishes an additional example of 

 a flower with a disagreeable odor, and a poor attendance, at least 

 so far as the number of individuals is concerned. Much time was 

 spent on this species during a vacation at Cedar Lake, Washington 



21) John H. Lovell, loc. cit. p. 452. 



22) P. Knuth. Handbuch d. Bluetenbiologie, Vol. II., p. 619, (enel. edit. 

 Vol. II., p. 622.) 



23) H. Mueller. Befruchtung d. Blumen durch Insekten, p. 397. 



