THEIR RELATION TO PLANTS 23 



For instance, the clovers are especially adapted to 

 attract long-tongued bees; flowers like the Petunia, 

 the evening primrose or the jimpson weed attract the 

 hawk-moths, whose long, flexible tongues reach to the 

 nectar cups at the very bottom of the deep florets. 



FIG. 6. a, Yucca flower with moth in position, ovipositing; &, Pronuba gath- 

 ering its pollen mass; c, head of Pronuba from side showing the maxillary 

 tentacle; d, tip of the ovipositor. 



So far as the insects are concerned the pollination 

 is a mere incident in most cases: it occurs because the 

 flower is so built that it must occur when the pollen or 

 nectar is gathered. But there is at least one case in 

 which it appears almost as if the insect acted intel- 

 ligently, with a definite purpose in view, and the 

 demonstration of this case we owe to the careful obser- 



