348 THE NATURALIST. 



opinion, that we have to explain ; but well and firmly established facts, ob- 

 tained by the ordinary methods of experiment, and which we fearlessly sub- 

 mit to the examination of all friends of science. We have simply to expound 

 what we have seen, experimented on, established ; that wliich those who feel 

 themselves most strongly disposed to contradict us, might have seen and 

 estabhshed as well as, and perhaps better than ourselves, had they under- 

 taken the same researches and the same experiments, with similar materials. 

 Indeed it is easy to understand, that when there exist, among plants observed 

 in the living state, and under perfectly analagous conditions of development, 

 manifest and easily recognisable differences, for any one who is capable of an 

 attentive examination ; to ascertain these differences is to ascertain a material 

 fact, upon the reality of which there cannot be two opinions. To ascertain 

 again, that these differences, visible one year, are still visible the following 

 year, and every year, is also a material fact of the same nature as the prece- 

 ding one. Lastly, to ascertam that the differences constantly offered by 

 divers individuals when compared together, are equally observable in other 

 individuals, the produce of the former, that they are reproduced hereditarily 

 and invariably during a succession of generations, is still proceeding in the 

 examination of a material fact, by searching whether it does or does not ex- 

 ist. Upon such a fact, properly observed, it is quite open for men of good 

 faith, to differ in opinion as to the consequences wliich they may draw from 

 it, but not as to the reality or non-reality of its existence. The species we 

 propose are nothing more than certain vegetable forms, which we have learned 

 to distinguish the one from the other, by a comparison, in the living state, 

 of all their organs, and by assuring ourselves, by the most rigorous observa- 

 tions, that their differences are hereditary, and not the result of accidental or 

 local causes. We say this of the great majority of our sj)ecies ; as to the 

 rest, we have judged them by the analogy of their characters, with those we 

 have been enabled to submit to experiment."* Thus, then, the sole criterion 

 admitted by M. Jordan, is the persistence of characters or differences, con- 

 tinued in seed, by generation. Every form which is preserved invariable for 

 a certain number of generations, is to him, a veritable species, it mattering 

 little if the differences which distinguish it from its congeners be reduced to 

 a mere trifle. To give his theory in a few words, as we read in his book, the 

 forms which remain stable after a culture of five, ten, fifteen, or twenty years, 

 are considered by him as distinct specific types. We say five to twenty years 



(4) Loc. cit., p. 6, 7. 



