iv ON PLANT LIFE 131 



same stock. They have been long known to 

 children and gardeners, who call them thrum- 

 eyed and pin-eyed. Mr. Darwin was the 

 first to explain the significance of this curious 

 difference. It cost him several years of 

 patient labour, but when once pointed out it 

 is sufficiently obvious. An insect thrusting its 



CO 



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X 250 



Fig. 12. Fig. 13. 



Flower and Pollen of Primrose 



proboscis down a primrose of the long-styled 

 form (Fig. 12) would dust its proboscis at a 

 part (a) which, when it visited a short-styled 

 flower (Fig. 13), would come just opposite 

 the head of the pistil (st), and could not fail 

 to deposit some of the pollen on the stigma. 

 Conversely, an insect visiting a short-styled 

 plant would dust its proboscis at a part farther 



