30 GEXERAL BIOLOGY 



by a nearly closed corolla entrance and by internal barri- 

 cades of spines, as to be accessible to only one kind of 

 visitors small worker bumblebees. A side view of a single 

 flower is shown in fig. 22a. The narrowly three-lobed, pro- 

 jecting lower lip offers an alighting place for the bees and 

 the reflexed edges of the corolla mouth offer them footholds. 

 A swollen palate upon the lower lip blockades the entrance 

 against other insects, but under the weight of the worker 

 bumblebee this is depressed sufficiently to allow the head 

 to be thrust into the median groove that divides the 

 "palate," and thereafter, a little pulling and pushing effects 

 an entrance. The queen bumblebee sometimes tries to 

 enter, but can only get her head inside: she is too big. 

 Other insects that are small enough are too light to "tip the 

 beam," or, entering, are barred from the nectar by a mat of 

 bristling hairs on the floor of the corolla and by dense 

 fringes of spines on the stamens: so that the worker 

 bumblebees have a monopoly. 



These bees serve the flower well. They exhibit a maximum 

 of efficiency in effecting cross pollination. The stigma of 

 the flower projects slightly beneath the tip of the upper lip 

 of the corolla. The pollen is carried by the bee in a great 

 quantity amid the hairs on the top of its prothorax. It will 

 be easily understood that in forcing an entrance through the 

 narrow passage, this pollen mass is pushed hard against the 

 stigma. A single visit is sufficient for complete pollination 

 of a flower. 



The chief means whereby the flower reserves its sweets 

 for proper visitors are not seen from the outside : and these 

 are its most peculiar and special devices, such as are taken 

 least into account in the preceding studies of this chapter. 

 So let us look within. Looking at the flower from below we 

 can see within the narrow corolla mouth the anthers stand- 

 ing close behind the tip of the pistil and close under the upper 



