Chap. IV.] NATURAL SELECTION. 75 



than others ; and thus the communities to which they belonged 

 would flourish and throw off many swarms inheriting the same 

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

 incarnate clovers (Trifolium pratense and incamatum) do not on 8 

 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 clover, which is visited by humble-bees alone ; so that 

 whole fields of the red clover offer in vain an abundant supply of 

 precious nectar to the hive- bee. That this nectar is much liked by 

 the hive-bee is certain ; for I have repeatedly seen, but only in the 

 autumn, many hive-bees sucking the flowers 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 are somewhat smaller, and that these are visited by 

 many hive-bees. I do not know whether this statement is accu- 

 rate; nor whether another published statement can be trusted, 

 namely, that the Ligurian bee, which is generally considered a 

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

 it, is able to reach and suck the nectar of the 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 the flowers, if humble- 

 bees were to become rare in any country, it might be a great 

 advantage to the plant to have a shorter or more deeply divided 

 corolla, so that the hive-bees should be enabled to suck its flowers. 

 Thus I can understand how a flower and a bee might slowly 

 become, either simultaneously or one after the other, modified and 

 adapted to each other in the most perfect manner, by the con- 

 tinued preservation of all the individuals which presented slight 

 deviations of structure mutually favourable to each other. 



I am well aware that this doctrine of natural selection, exempli- 

 fied in the above imaginary instances, is open to the same objections 

 which were first urged against Sir Charles Lyell's noble views on 

 " the modern changes of the earth, as illustrative of geology; " but 

 we now seldom hear the agencies which we see still at work, spoken 

 of as trifling or insignificant, when used in explaining the excavation 

 of the deepest valleys or the formation of long lines of inland 

 cliffs. Natural selection acts only by the preservation and accumu- 

 lation of small inherited modifications, each profitable to the pre- 

 served, being ; and as modern geology has almost banished such 



