blossom Hosts and Insect Guests 



conditions necessary to its perpetuation. The floral 

 adaptation is such that the moth must force its large 

 head far into the opening of the blossom ni order 

 to reach the sweets in the long nectary. In so doing 

 the pollen becomes attached to the base of the 

 tongue, and is withdrawn as the insect leaves the 

 flower, and is thrust against the stigma in the next 

 blossom visited. This was clearly demonstrated by 

 Darwin in specimens sent to him, by means of a 

 probe of the presumable length and diameter of the 

 moth's tongue. Shorter-tongued moths would fail to 

 remove the pollen, and also to reach the nectar, and 

 would thus soon cease to visit the blossom. 



HOW X AT URAL SELECTION PERFECTS THE AXGRJECUM 



The Angraecum also affords in this long pendent 

 nectary a most lucid illustration of the present work- 

 ings of natural selection. The normal length of 

 that nectary should be about eleven inches, but, in 

 fact, this length varies considerably in the flowers 

 of different plants. 



Let us suppose a flower whose nectary chances 

 to be only six inches in length. The moth visits 

 this flower, but the tip of its tongue reaches the nectar 

 long before it can bring its head into the opening 

 of the tube. This being a vital condition, the moth 

 fails to withdraw the pollen ; and inasmuch as the 



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