116 ILLUSTRATIONS OP THE ACTION OP [Chap. IV. 



has 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 

 sometimes the female organs become more or less im- 

 potent; 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 advantage- 

 ous on the principle of the division of labour, individ- 

 uals with this tendency more and more increased, would 

 be continually favoured or selected, until at last a com- 

 plete separation of the sexes might be effected. It 

 would take up too much space to show the various steps, 

 through dimorphism and other means, by which the 

 separation of the sexes in plants of various kinds is ap- 

 parently 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 dioeciously 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. Bear- 

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

 certain circumstances individual differences in the cur- 



