1909] Graenicher, Wisconsin Flowers and Their Pollination. 31 



TUBE LENGTH. 



All of the species of Composite dealt with belong to the Tub- 

 uliflorse, in other words the inflorescence is made up entirely of 

 tubular florets, as in Eupatorium, Liatris, Antennaria, Tan- 

 acetum, Cacalia, Arctium and Cirsium, or at least in its central 

 portion, the so-called disk. In those species in which ray florets 

 are present, the latter contain neither nectar nor pollen. For this 

 reason insects visiting such inflorescences in search of food con- 

 fine their attention to the tubular florets, and we shall therefore 

 consider the length of the tube of these florets in our endeavor to 

 determine the effect of tube length on the make-up of the visitors. 



The corolla of a tubal floret consists in most cases of two 

 distinct parts, a lower narrow portion, and an upper distended 

 portion with its five lobes. Owing to its narrowness, and to tht 

 additional fact that in mariv instances its lumen is more or less 

 taken up by the style and the five filaments, there is little or no 

 room left in the lower portion for the reception of the insect's 

 tomrue. In such florets the latter is therefore not able to advance 

 farther than to the bottom of the upper portion. Nectar is secreted 

 at the base of the lower part, but it rises in the latter, and accum- 

 ulates at the bottom of the upper widened part, where it is acces- 

 sible to tongues possessed of the necessary length to reach it. This 

 upper part, from the middle of which the anther-cylinder enclos- 

 ing the stylar branches protrudes, presents the shape of a cup, a 

 bell, or a cylinder, according to the increase of length over width. 

 As stated above the length (depth) of this part of the corolla de- 

 termines in many florets, as for example in Eupatorium, Aster, 

 Solidago, Erigeron, Cacalia, Arctium and Cirsium, the depth to 

 which an insect's tongue can penetrate, and in such cases the 

 figures given further on for tube length refer to the length of this 

 upper portion. 



A comparison of the results obtained in the 9 species of Aster 

 studied shows how along with the increase in tube length there 

 is in general an increase in the percentage of long-tongued in- 

 sects, and a decrease in the percentage of the short-tongued ones. 

 The difference in color of the rays in the different species will be 

 considered in the course of this paper. 



