174 NATURAL SCIENCE [September 



countenance to Darwin's idea, that a species must have a numerous 

 population to produce varieties, the rule seems rather to he that 

 these two features do not necessarily coincide at all. 



Supposed Aids to Natural Selection. — In order to secure 

 the survival of the fittest, i.e., a new variety among the parent form, 

 it was perceived that two additional and hypothetical aids were 

 necessary, viz., (1) some degree of infertility with the parent, and 

 (2) a rapidity of adaptation. 



With regard to the first, all experience goes to prove that it 

 does not exist ; for when cultivators wish to fix a new race, as of 

 cabbage, &c, they are obliged to grow it as far as possible away 

 from the parent stock. Indeed, considering how freely species can 

 be hybridised, the probability of an offspring refusing to be crossed 

 by the same species is very small or nil. Neither Darwin nor Dr 

 Wallace bring forward any examples of infertility with the parent 

 among plants. 



Secondly, a rapidity of adaptation is claimed hypothetically. 

 This does often really exist, but it is a little uncertain whether 

 these authors were aware of it. For when a plant finds itself in a 

 new and markedly different environment, which strongly affects it, 

 it then grows by self-adaptation in response to the new external 

 influences : as when passing from water to land, or vice versa ; from 

 the wild state to the artificial soil of a garden ; from lowlands to 

 alpine or subarctic localities, &c, as I have shown in " The Origin of 

 Plant Structures." 



The Persistence or non-retention of new varietal 

 characters. — To come to what Dr Wallace regarded as the 

 most important point in his paper. Four times does he mention 

 it, only slightly altering the expression, e.g., he says: — " No attempt 

 has been made to show, even hypothetically, how, through the 

 action of known causes, such characters [useless ones], when they 

 do arise, can become first extended to every individual of a species, 

 and then be totally obliterated as regards any portion of the species 

 which may become modified so as to constitute a. new species. 

 Useful characters thus strictly limited are the necessary and 

 logical results of modification through survival of the fittest. No 

 agency has been shown to exist capable of producing useless 

 characters similarly limited." l As illustrations to meet Dr Wal- 

 lace's demand, it may be observed that the races of cultivated 

 pears are spineless ; yet they are derived from the wild Pyrus 

 communis, which has useless abortive branches as spines. Similarly 

 is it the case with some varieties of plums derived from Prunus 

 communis. 



With regard to the retention of injurious characters, the 



1 Loc. cit., \\ 491. 



