PEOF. CRBPIN : CONSIDERATIONS ON " SPECIES." 



13 



rigourously concluded to be indefinitely stable and cannot be admitted 

 with, certainty as a species. 



xvi. — In order to admit to the title of a veritable species, any form remaining 



persistent after five, ten, fifteen, or twenty successive generations, it is 

 requisite that it should be proved that every variety and every variation — 

 unless the existence of such be denied — returns to its type after the first 

 or second generation, or is seen to modify its characters. 



xvii. — We cannot deny the possibility of the existence of varieties, persisting 

 with their differences, for a longer or shorter time. 



xviii — A great number of the species of the new school do not even repose 

 on the proofs of cultivation, and the only guarantee for their legitimacy 

 is simply analogy. 



xix.— The stability of certain species of the new school is contradicted by 



experiments made by the Linnean school. 

 XX. — In the actual state of science, we cannot, /rom the present time, consider 



the great majority of species, be they of the Linnean or of the new 



school, but as provisional specific types. 



xxi. — We cannot admit the species created by the two schools as irreducible 



types, in our own age — our own geological period — until a very great 

 number of experiments on their cultivation have been made, not solely 

 by a few experimenters, but by a multitude of observers belonging to 

 both schools : the results of which expermients should agree together. 



xxii. — As of all the practical criteria wliich have been extolled so far there is 

 but one really practicable — that founded upon essays in cultivation — we 

 ought most carefully to attach ourselves to it. 



xxiii. — In default of proofs furnished by cultivation, we may with advantage 

 have recourse to the profound study of transitory forms. 



xxiv. — When two forms are connected together by other intermediate forms 

 (not hybrids) establishing a gradual and insensible passage from one to 

 the other, we are to a certain extent right in assuming that they con- 

 stitute but one species, the individuals of which oscillate between certain 

 limits. 



XXV. — Hybridism may also furnish proofs, to strengthen those derived from 

 cultivation, but besides, that it presents great difficulties, some extra- 

 ordinary facts have recently been brought to light, upsetting the ideas 

 which have been admitted upon its results. 



