300 ORIGIN OF SPECIES 



Gartner gives in his table about a score of cases of plants 

 which he castrated, and artificially fertilised with their own 

 pollen, and (excluding all cases such as the Leguminosae, in 

 which there is an acknowledged difficulty in the manipula- 

 tion) half of these twenty plants had their fertility in some 

 degree impaired. Moreover, as Gartner repeatedly crossed 

 some forms, such as the common red and blue pimpernels 

 (Anagallis arvensis and cceulea), which the best botanists 

 rank as varieties, and found them absolutely sterile, we may 

 doubt whether many species are really so sterile, when inter- 

 crossed, as he believed. 



It is certain, on the one hand, that the sterility of various 

 species when crossed is so different in degree and graduates 

 away so insensibly, and, on the other hand, that the fertility 

 of pure species is so easily affected by various circumstances, 

 that for all practical purposes it is most difficult to say where 

 perfect fertility ends and sterility begins. I think no better 

 evidence of this can be required than that the two most ex- 

 perienced observers who have ever lived, namely Kolreuter 

 and Gartner, arrived at diametrically opposite conclusions in 

 regard to some of the very same forms. It is also most in- 

 structive to compare — but I have not space here to enter into 

 details — the evidence advanced by our best botanists on the 

 question whether certain doubtful forms should be ranked as 

 species or varieties, with the evidence from fertility adduced 

 by different hybridisers, or by the same observer from ex- 

 periments made during different years. It can thus be shown 

 that neither sterility nor fertility affords any certain distinc- 

 tion between species and varieties. The evidence from this 

 source graduates away, and is doubtful in the same degree as 

 is the evidence derived from other constitutional and struc- 

 tural differences. 



In regard to the sterility of hybrids in successive genera- 

 tions ; though Gartner was enabled to rear some hybrids, care- 

 fully guarding them from a cross with either pure parent, for 

 six or seven, and in one case for ten generations, yet he 

 asserts positively that their fertility never increases, but gen- 

 erally decreases greatly and suddenly. With respect to this 

 decrease, it may first be noticed that when any deviation in 

 structure or constitution is common to both parents, this is 



