342 THE EVOLUTION THEORY 



been made available to all. Future investigations and studies must 

 throw more light upon the problem. 



In any case, however, we can see from the frequency of mutual 

 fertility among plants that mutual sterility is not a conditio sine qua 

 non of the splitting up of species, and we must beware of laying too 

 great stress upon it even among animals. Germinal selection is 

 a process which not only forms the basis of all personal selection, but 

 which is also able to give rise of itself, without the usual aid of sexual 

 intermingling, to a new specific tj^pe. And we cannot with any 

 confidence dispute that, even without amphigony, a certain degree of 

 personal selection may not ensue solely on the basis of the favourable 

 variational departures originating in the germ-plasm. It would be 

 premature to express any definite views on this point as yet, but the 

 diverse cases of purely asexual or parthenogenetic reproduction 

 in groups of plants rich in species make this hj^pothesis seem 

 probable. 



The most remarkable example of this is probably to be found in 

 the Lichens, the symbiotic nature of which we have already discussed, 

 in which — now at least — neither the Fungus nor the Alga associated 

 with it is known to exhibit sexual reproduction. If this is really 

 the case, then the existence of numerous and well-marked species 

 of lichens leads us to the hypothesis just expressed, and we must 

 suppose that the unity of the specific type is attained in this case 

 solely by a continual sifting of the useful from the useless variations 

 of the determinants, and through purely germinal intensification of 

 the surviving variational tendencies. 



Of course it is possible that the mutual adaptation of the Algae 

 and Fungi in the evolution of species of Lichens took place very long 

 ago, at a time when sexual reproduction still existed, at least in one 

 of the associated organisms, the Fungus. The Ascomycetes, to which 

 most of the Lichens belong, do not at present usually exhibit the 

 process of amphimixis, as I have already noted ; but it may perhaps 

 be still possible to decide whether they must have exhibited it, or at 

 least could have exhibited it at an earlier stage in their evolution. 

 As the group of Thallophytes is a very ancient one, it is not incon- 

 ceivable that the modern species of Lichens have existed for a long 

 time, and that they had their origin in the remote past with the 

 assistance of amphimixis. 



Nor need it be objected to this supposition that it has been found 

 possible to make new Lichens by bringing together Fungi and Algce 

 which had not previously been associated witli one another ; for in 

 the first place both were already adapted to partnership with other 



