THE FLOWER AND THE BEE 



flow entirely ceases and the bees promptly discontinue their 

 visits. "In spite of the shimmering sea of flowers, in spite of 

 the strong fragrance, only a few bees can be found in the buck- 

 wheat-field after twelve o'clock." Again, a sudden shower fol- 

 lowed by a fall in temperature may bring the buckwheat 

 harvest to an abrupt and premature close in August, when or- 

 dinarily it would continue into September. The bees then 

 immediately cease visiting the flowers and in countless num- 

 bers attempt to rob each other; the time of their visits thus 

 always coincides with the period of active secretion of nectar. 

 (Fig. 46.) 



The rapidity with which bees visit flowers is greatly influenced 

 by their form and arrangement. Honey-bees cannot reach 

 the nectar of the yellow and red garden-nasturtiums, which lies 

 at the bottom of a long calycine spur and, consequently, are 

 seldom seen on the flowers, although occasionally they come for 

 pollen. One of the larger bumblebees {Bombus fervidus), which 

 has a tongue 12 mm. long, on the contrary devotes itself ex- 

 clusively to sucking nectar and ignores the pollen. It is rather 

 clumsy in its movements and visits only from 1*2 to 14 flowers 

 per minute. The bilabiate flowers of the pickerel-weed {Ponte- 

 deria cordaia) are examined much more rapidly by a smaller 

 species of bumblebee {Bombus vagans). In July the violet-blue 

 spikes of this aquatic plant fringe the banks of many northern 

 streams in countless numbers. Bombus vagans is a very common 

 visitor, beginning always with the lowest flowers of the spike 

 and working upward. By actual count, several times re- 

 peated, I found that the average number of visits per minute 

 was about 70. The small florets of the goldenrods are visited 

 so rapidly that the number per minute cannot usually be 

 counted. But when the nectar is very abundant, as in the 

 flowers of the basswood, century -plant, spider-plant (Cleome 



90 



