Progression^ Retrogression and Degression. 65 



I think it undesirable that these two types of sub- 

 divisions of the species should continue to be denoted 

 by the same term. The simplest plan would be to refer 

 to the former as elementary species and only to the latter 

 as varieties, and I hope that this limitation of the terms 

 will come into general use. 



The question, however, is a purely systematic one and 

 belongs to the department of descriptive science. For as 

 soon as it is treated from the experimental standpoint 

 the whole difference disappears. Many of the best vari- 

 eties prove, when tested by sowing, to be as constant as 

 elementary species, so that a separation on the basis of 

 constancy is out of the question. 



* * * 



On the basis of the foregoing discussion I treat the 

 homonomous subdivisions of the Linnean species as 

 elementary species and eventually denote them with bi- 

 nary names. In the case of derivative varieties, however, 

 I prefer to make no definite choice ; I regard for example 

 ChcHdoniiun laciniatiun Miller and Chelidoniuni majus 

 laciniatuni as equally justifiable. And when for instance 

 several species in the same genus have white flowered or 

 glabrous varieties, a binary nomenclature would obviously 

 be much too cumbrous.^ 



§ 7. PROGRESSIVE, RETROGRESSIVE AND DEGRESSIVE 



FORMATION OF SPECIES. 



A glance at the phylogeny of the vegetable kingdom 

 reveals the fact that all species cannot have arisen in the 

 same way. Progressive development is due to the con- 



^ For instance if specific names like that of Agrostemma nicae- 

 cnsis for Agrostemma Githago pallida were generally used for white 

 flowered varieties. 



