70 ON THE INTERCROSSING [CHAP. IV. 



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 some- 

 what 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 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 continued pre- 

 servation 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, 

 exemplied 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, spokf-n 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 accumulation of small inherited modifications, 

 each profitable to the preserved being ; and as modern geology has 

 almost banished such views as the excavation of a great valley by 

 a single diluvial wave, so will natural selection banish the belief 

 of the continued creation of new organic beings, or of any great 

 and sudden modification in their structure. 



On the Intercrossing of Individuals. 



I must here introduce a short digression. In the case of animals 

 and plants with separated sexes, it is of course obvious that two 

 individuals must always (with the exception of the curious and 

 not well understood cases of parthenogenesis) unite for each 

 birth ; but in the case of hermaphrodites this is far from obvious. 

 Nevertheless there is reason to believe that with all hermaphro- 

 dites two individuals, either occasionally or habitually, concur for 

 the reproduction of their kind. This view was long ago doubtfully 

 suggested by Sprengel, Knight and Kolreuter. We shall presently 



