1909] Graenicher, Wisconsin Floicrrs ami Their Pollination. 33 



Tube length Average number 

 of visitors. 



1 1 species y 2 — 1 mm. 86 



12 " iy 4 — 2 mm. 76 



4 " 2y 2 — 3 mm. 68 



3 " 3%— 4 mm. 47 



5 " 4y 2 — 5 mm. 42 



2 " 6 mm. 29 



Erigcron canadensis with its extremely small florets has the 

 shortest tube (}/> mm.) among our Compositse. No eutropous 

 visitors figure on its list, and the allotropous (56.9%) outnumber 

 the hemitropous visitors (43.1%). The allotropous visitors are 

 also in the majority on the flowers of Aster lateriHorus, and of all 

 of our native species blooming in summer, whose tube length does 

 not exceed 1 mm. In Aster panicnlatus (tube length i)A. mm.) 

 on the other hand the hemitropous visitors (554%) predominate, 

 and this is the case in all of our species with longer tubes. The 

 flowers of Antennaria neglecta, the earliest of our Compositae ap- 

 pear in the spring, and have a tube agreeing in length (1 mm.) 

 with that of Aster lateriflorus, etc.. but they show quite a differ- 

 ence in the make-up of their visitors. In Antennaria neglecta the 

 hemitropous (63.6%) outnumber the allotropous visitors (31.8%) 

 while in Aster lateritiorus etc., the opposite is the case. Our an- 

 thophilous insect- fauna of early, spring differs in many points 

 from that of the summer months. During the flowering season 

 of Antennaria neglecta none of the 52 allotropous solitary wasps 

 are on the wing that figure so prominently as visitors of our 

 asters, goldenrods, etc. The allotropous flies of the family Tachi- 

 nid?e are represented in the general list of visitors of the Com- 

 positse to the number of 46. and only 4 of these appear early 

 enough to pay their attention to the flowers of Antennaria neg- 

 lecta. These facts explain the difference in the proportion of 

 allotropous to hemitropous visitors in those vernal and aestival 

 flowers that otherwise agree in structure and dimensions (tube 

 length). In other words the proportion of poorly adapted to more 

 adapted visitors is determined not by the characters of the flower 

 alone, but also by the composition of the anthophilous insect-fauna 

 to which the flower is exposed, and this is subject to seasonal 

 changes. 



COLOR. 



At the beginning of this paper I have called attention to the 

 difference of opinion among the various observers as to the effect 

 of the colors of flowers on the insect visitors. The evidence pro- 



