THE ARETHUSA. 45 



bottom turned toward the end of the petal and fastened to it by a 

 delicate hinge of vegetable tissue. This brings the open top of 

 the cup toward the inner part of the flower. The mouth of the 

 cup is closed up by a thin partition drawn across the little furrow 

 in which it lies. The other or inside of this partition is the stigma 

 of the flower. 



It is not difficult to see that the two parts are so adjusted 

 to each other as to make it in the highest degree difficult, if not 

 altogether impossible, for the pollen unaided to come in contact 

 with the stigma. But with the aid of a bee in search of honey 

 it is very easily accomplished. The bee lights upon the downy 

 hanging platform of the "labellum," and proceeds to make his 

 way down the throat of the flower to the nectar. In doing so 

 he might run his head against the projecting anther cup, but of 

 course could not move it, for it is so hinged that it will turn 

 outward and not inward. 



But on his way out the bee again knocks his head against 

 the little cup, and this time it responds to his lightest touch. 

 It immediately swings out and opens downward, and spills its 

 little bundles of pollen directly upon the top of the bee's head 

 or back, and they stick fast. The very next Arethusa he visits 

 and comes out of he will be sure to leave some of this pollen 

 upon the stigmatic surface just where it is needed to fructify the 

 flower. He will at the same time carry away more pollen from 

 this flower wherewith to pollenize the next one, and so on. The 

 service rendered by insects in cross-fertilizing plants, thus mak- 

 ing them more prolific and more vigorous, is coming to be one 

 of the most interesting and important fields for investigation in 

 the natural history of the vegetable kingdom. One sees, also, 



