INSECTS AND FLOWERS 455 



long, and the cavity of the tube is closed at about the middle 

 of its length by the insertion of filaments there. When the 

 flower opens in the evening it emits a strong musky odor, 

 and a large drop of nectar is already present in the bottom 

 of the tube; so that large sphinx moths, leaving the places 

 of seclusion occupied by them during the day, are attracted 

 by the strong odor and white color of the flowers. 



"Flying swiftly from flower to flower, the moth thrusts 

 its long proboscis to the bottom of the tube and secvires the 

 nectar; and while it is tarrying briefly at each flower, keeping 

 itself poised by the swift vibration of .its wings, it is pretty 

 certain to touch with its proboscis both anthers and stigmas, 

 which stand close together at about the same height near 

 the mouth of the corolla. Both cross- and self-pollination 

 might be brought about in this way, but as Darwin has 

 shown, the foreign pollen would probably possess the greater 

 potency, and cross-fertilization would be apt to result. 

 The harmonious relation between length of the insect pro-' 

 boscis and depth of the flower corolla is strikingly shown 

 by all the sphinx moths and the flowers they visit. 



Another kind of arrangement of flower structure which 

 tends to preserve the nectar for certain special kinds of 

 insects is well illustrated by the salvias, snap-dragon, and 

 other similar flowers. In these the corolla is irregular and 

 the stamens and pistils are so arranged that insect visitors 

 are compelled to visit the nectary in one particular manner, 

 a manner such as to insure their touching the anthers or 

 stigma or both. In the snap-dragon the opening of the 

 flower-cup is normally closed, but when a bee alights on the 

 broad keel or platform (composed of two petals grown 

 together) its weight so depresses this platform as to open 

 the way into the flower-cup, which closes at once when the 

 bee goes in and drinks the nectar. Scrambling and twisting 

 about in the narrow chamber it thus thoroughly dusts itself 

 with pollen^ or thoroughly dusts the stigma with pollen 



