Chap. IV. NATUKAL SELECTION. 97 



but I may add that .some of the species of holly in North 

 America are, accordiiifj to Asa Gray, in an intermediate con- 

 dition, or, as he cxpixvsses it, arc more or less diceciously po- 

 lygamous. 



Let us now turn to the nectar-feeding insects. We may 

 suppose the plant, of which we have been slowly increasing 

 the nectar hy continued selection, to be a common plant ; and 

 that certain insects depended in main part on its nectar for 

 fooil. 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 troul)le, enter by the mouth. 

 Bearing such facts in mind, it may be believed that, under cer- 

 tain circumstances, individual differences in the curvature or 

 length of the proboscis, etc., too slight to be appreciated by 

 us, might profit a bee or other insect, so that certain individ- 

 uals would be able to obtain their food more quickly than 

 others ; and thus the communities to which they belonged 

 would ilourish and throw off many swarms inheriting the same 

 peculiarities. The tulles of the corolla of the common red and 

 incarnate clovers (Trifolium pratense and incarnatum) do not 

 on a hasty glance appear to differ in length ; yet the hive-bee 

 ran easily suck the nectar out of the incarnate clover, but not 

 out of the common red clover, Avhich is visited by humble-bees 

 alone ; so that whole fields of the red clover in vain offer an 

 abundant supply of precious nectar to the hive-bee. Tliat this 

 nectar is much liked by the hive-bee is certain ; for I have re- 

 ])eatedly seen, but only in the autumn, many hive-bees sucking 

 the (lowei-s through holes bitten in the base of the tube by 

 humble-bees. The difference in the length of the corolla in 

 the two kinds of clover, which determines the visits of the 

 hive-bee, must be very trifling ; for I have been assured that 

 when red clover has been mown, the flowers of the second crop 

 nve somewhat smaller, and that these are visited by many 

 hive-bees. I do not know whether this statement is accurate; 

 nor whether another published statement can be trusted, namely, 

 that the Ligurian bee, which is generally considered a mere 

 variety and which freely crosses with the common hive-bee, is 

 able to. reach and suck the nectar of the connnon red clover. 

 Thus, in a country where this kind of clover abounded, it might 

 be a great advantage to the hive-bee to have a slightly-longer 

 or differently-constructed proboscis.. On the other hand, as 

 the fertility of this clover absolutely depends on bees visiting 



