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



always more or less incomplete, even in such cases where it repre- 

 sents the results of very careful, and often repeated observations. 

 Another fact to be considered is that there is a varying percentage 

 of pollen-eating, short-tongued visitors at flowers, the tube length 

 of which excludes them from obtaining nectar. Their presence 

 has nothing to do with tube length, but their number figures in the 

 list, and the percentages representing the proportion of short- to- 

 long-tonsmed visitors obtained from such a list are not indicative 

 of the effect of tube length alone. 



According to the figures contained in the two tables above the 

 percentages for the long-tongued bees (eutropous) show a more 

 rapid increase of visits to flowers with shorter tubes, i. e., tubes 

 below 4 mm. in length than those for the butterflies, and moths 

 (Lepidoptera). From 4 mm. on the visits of the latter insects as- 

 sume greater proportions, and the percentage of their visits to the 2 

 thistles of the genus Cirsium with a tube length of 6 mm. nearly 

 equals that of the long-tongued bees. The butterflies and moths 

 favor flowers with long and narrow tubes, and we may well un- 

 derstand, how a steady increase in tube length in our Compositae 

 might produce typical butterfly-flowers, in which the nectar would 

 be inaccessible to even the longest tongues among our bees. 



In closing our remarks on the effect of tube length, it may be 

 stated that, according to the results obtained from a study of our 

 Compositae the proportion of short-tongued to long-tngued visitors- 

 in these flowers is determined by tube length more than by any 

 other character of the flower. The number of visitors, in species as 

 well, as in individuals, depends on tube length (decrease in number 

 with increase in tube length), as also on other floral characters, 

 such as odor, supply and taste of pollen and nectar ( insects possess 

 a "grs'jatory memory," as pointed out by Forel 24 ) and color. As 

 regards the latter, the evidence procured from our observations of 

 the Compositae is not favorable to Mueller's theory of color pre- 

 ference. 



PART 2. 



This rnrt contains an account of the blooming period, struc- 

 ture, rel.-'tions to insects, etc., of the flowers of the 37 species of 

 Compositae, considered in this paper. As previously stated (p. 21 ) 

 a number in the list of visitors accompanying a discussion of each 

 plant-species, refers to a species of insect bearing that number in 

 the general list of visitors ( pp. 2 1 -27 ) . 



24) A. Forel. The senses of insects. Engl, transl. by Macleod Tearsley. 



