116 ILLUSTEATIONS OF THE ACTION OF [Chap. IV. 



been called the "physiological division of labour ; " hence 

 we may believe that it would be advantageous to a plant 

 to produce stamens alone in one flower or on one whole 

 plant, and pistils alone in another flower or on another 

 plant. In plants under culture and placed under new 

 conditions of life, sometimes the male organs and some- 

 times 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 might he effected. It would take up too 

 much space to show the various steps, through dimor- 

 phism and other means, by which the separation of the 

 sexes in plants of various kinds is apparently now in 

 progress ; but I may add that some of the species of 

 holly in North America, are, according to Asa Gray, in 

 an exactly intermediate condition, or, as he expresses it, 

 are more or less diceciously polygamous. 



Let us now turn to the nectar-feeding insects ; 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 insects 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 with a very 

 little more trouble, they can enter by the mouth. Bearing 

 such facts in mind, it may be believed that under certain 

 circumstances individual differences in the curvature or 



