CLASSIFICATION. 399 



scheme, the great composite family of plants, together 

 with the closely approximate genus Jasione, are first 

 separated from all other flowering plants by the compound 

 character of their flowers. The remaining plants are sub- 

 divided according as the perianth is double or single. 

 Since no plants are yet known in which the perianth can 

 be said to have three or more distinct rings, this division 

 becomes practically the same as one into double and not- 

 double. Flowers with a double perianth are next discrimi- 

 nated according as the corolla does or does not consist of 

 one piece, according as the ovary is free or not-free, as it 

 is simple or not simple, as the corolla is regular or irre- 

 gular, and so on. On looking over this arrangement, it 

 will be found that numerical discriminations often occur, 

 the numbers of petals, stamens, capsules, or other parts 

 being the criteria, in which cases, as already explained 

 (vol. ii. p. 374), the actual exhibition of the bifid division 

 would be tedious. 



Linnseus appears to have been perfectly acquainted 

 with the nature and uses of diagnostic classification, which 

 he describes under the name of Synopsis, saying : 

 'Synopsis tradit Divisiones arbitrarias, longiores aut brevi- 

 ores, plures aut pauciores : a Botanicis in genere non 

 agnoscenda. Synopsis est dichotomia arbitraria, quas 

 instar vise ad Botanicem ducit. Limites autern non deter- 

 minat.' 



The rules and tables drawn out by chemists to facilitate 

 the discovery of the nature of a substance in qualitative 

 analysis are usually arranged on the bifurcate method, 

 and form excellent examples of diagnostic classification, 

 the qualities of the substances employed in testing being 

 in most cases merely characteristic properties of little 

 importance in other respects. The chemist does not detect 

 potassium by reducing it to the state of metallic potas- 

 c 'Philosophia Botanica' (1770), 154, p. 98. 



