94 NATUKAL SELECTION. Chap. IV. 



another flower or on another plant. In plants under 

 culture and placed under new conditions of life, some- 

 times the male organs and sometimes the female organs 

 become more or less impotent ; now if we suppose this to 

 occur in ever so slight a degree under nature, then as 

 pollen is already carried regularly from flower to flower, 

 and as a more complete separation of the sexes of our 

 plant would be advantageous on the principle of the 

 division of labour, individuals with this tendency more 

 and more increased, would be continually favoured or 

 selected, until at last a complete separation of the sexes 

 would be effected. 



Let us now turn to the nectar-feeding insects in our 

 imaginary case : we may suppose the plant of which 

 we have been slowly increasing the nectar by continued 

 selection, to be a common plant ; and that certain in- 

 sects depended in main part on its nectar for food. I 

 could give many facts, showing how anxious bees are 

 to save time ; for instance, their habit of cutting 

 holes and sucking the nectar at the bases of certain 

 flowers, which they can, with a very little more trouble, 

 enter by the mouth. Bearing such facts in mind, I can 

 see no reason to doubt that an accidental deviation in 

 the size and form of the body, or in the curvature and 

 length of the proboscis, &c, far too slight to be appre- 

 ciated by us, might profit a bee or other insect, so that 

 an individual so characterised would be able to obtain 

 its food more quickly, and so have a better chance of 

 living and leaving descendants. Its descendants would 

 probably inherit a tendency to a similar slight deviation 

 of structure. The tubes of the corollas of the common 

 red and incarnate clovers (Trifolium pratense and in- 

 carnatum) do not on a hasty glance appear to differ in 

 length ; yet the hive-bee can easily suck the nectar out 

 of the incarnate clover, but not out of the common red 



