132 THE NATURALIST IN NICARAGUA. [Ch. Till. 



flower, and ascending step by step to the highest. The 

 four stamens and the pistil of the foxglove are laid 

 closely against the upper side of the flower. First a 

 stamen on one side opens its anthers and exposes its 

 pollen. The humble-bee, as it bustles in, brushes this 

 off. Then another stamen exposes its pollen on the 

 other side, then another and another ; but not till all the 

 pollen has been brushed off does the cleft- end of the 

 pistil open, and expose its viscid stigma. The humble- 

 bee brushes off the pollen into its hairy coat from the 

 upper flowers of one raceme and carries it direct to the 

 lowest flowers of another, where the viscid stigmas are 

 open and ready to receive it. If the humble-bee went 

 first to the upper flowers of the spike and proceeded 

 downwards, the whole economy of this plant to procure 

 cross fertilisation would be upset.* The open flower of 

 the foxglove hangs downwards. The lower part, or 

 dilated opening of the tube, is turned outwards, and has 

 scattered stiff hairs distributed over its inner surface ; 

 above these the inside of the flower hangs almost perpen- 

 dicularly, and is smooth and pearly. The large humble- 

 bee bustles in with the greatest ease, and uses these hairs 

 as footholds whilst he is sucking the honey; but the smaller 

 bees are impeded by them, and when, having at last strug- 

 gled through them, they reach the pearly, slippery precipice 

 above, they are completely bafBed. I passed the autumn 



* Darwin mentions having seen humble bees visiting- the flower- 

 ing spikes of the Spiranthes autumnalis (ladies' tresses), and notices 

 that they always commenced with the bottom flowers, and crawling 

 spirally up sucked one flower after the other, and shows how this . 

 proceeding ensures the cross fertilisation of different plants. " Fer- 

 tilisation of Orchids," 127. 



