108 ON VARIETIES, KACES, SUB-SPECIES, AND SPECIES. 



tlie earth ; it is from this time that, conformably to our actual 

 knowledge, we have expressed our belief in the immutability of 

 species without speculating on their existence or non-existence in 

 the ages preceding that epoch, and without deciding what they 

 may hereafter become. 



We attach great importance to the subordination of the dif- 

 ferent groups of individuals distinguished into simple varieties, 

 races, and sub-species. If we have not given any new mode of 

 limiting these groups, we hope that, at all events, the manner in 

 which we have examined and defined them will add somewhat to 

 their precision, and that the naturalist who may endeavour to 

 apply to the individuals of a given species the distinctions above 

 pointed out, will be led to examine many points connected with 

 the species which would not perhaps otherwise have suggested 

 themselves to his mind ; and we further hope that by appending 

 the signs of these distinctions to the species of plants and ani- 

 mals as they are examined, their descriptions will be found to 

 be considerably more precise than they at present are. 



Whilst considering useful plants with respect to the stability 

 of their essential characters, and also with respect to their ten- 

 dency to become modified by a change of circumstances in which 

 they live, we have found it sufficient to recall to the reader's re- 

 membrance the considerations and definitions previously laid 

 before him, because the study of the changes in the individuals 

 of a species itself furnished arguments in favour of our definition 

 of species viewed generally with respect to the organization of 

 its individual members, and of the circumstances in which they 

 were placed. 



This then is the conclusion to which we arrive after examin- 

 ing the changes of which plants are susceptible when propagated, 

 1, by seed; 2, by hybridizing ; 3, by division. 



1. By seed. — The modifications which can be produced in 

 plants propagated by seed take place whilst the seed itself is 

 forming, and during the development of the plant sprung from 

 that seed. The modifications arise from organization and from 

 external causes: these causes are essential, and differ from those 

 occasional ones which arise from artificial methods of cultiva- 

 tion, and which may sometimes work concurrently with them. 



2. By hybridizing . — An examination of the results thus ob- 

 tained, far from being favourable to the principle of immuta- 

 bility, has revealed facts which are conformable to the opposite 

 principle, as we have found hybrids which die out or separate 

 into two individuals, which existed rather side by side than 

 merged the one in the other. 



3. By division. — A^\how^\\ it is true that plants propagated 



