204 The Origin of Species by Mutation. 



the females have increased in number in proportion to 

 the males. This was observed by Hoffmann on Spi- 

 nacia, Rvunex and LycJinis, and by others on many other 

 species. In Matthiola incana the strongest seeds give 

 double-flowered individuals but the proportions of such 

 depend on the conditions in which they are cultivated ; 

 when seeds are gathered in the open they do not exceed 

 50%, when sown in puts they attain 60 and sometimes 

 70%. 



It seems to me therefore to be a warrantable assump- 

 tion that in geological times many newly arisen forms 

 were promptly anniliilated and have left no trace. 



If the hypothesis of mutability in one direction ren- 

 ders the theory of a selection operating in a constant 

 direction superfluous, then we must regard mutations 

 as in a very high degree limited. Only those species, 

 whose remains have been found in paleontological strata 

 could have arisen by it ; and strictly speaking only those 

 wliich lav in the direct line of descent. All lateral 

 branches which have died without posterity point to a 

 selection operating continually in the direction of the 

 main line of descent. It seems to me that the more we 

 consider Scott's view in detail the more do the differ- 

 ences between him and Darwin tend to disappear. 



The question how far the theory that selection may 

 have operated in one direction during long periods of 

 time is justified lies outside the scope of this book : but 

 it will be admitted first, that it has never been proved to 

 be false, and secondly, that this theory has at least as much 

 justification as that of mutability in one direction. 



In short: The mutation theory demands that organ- 

 isms should exhibit mutability in almost all directions. 

 The facts of paleontology and classification are in accord 



