I.] CLASSIFICATION. 127 



each other are said to be diag?iostic. The (hagnostic cha- 

 racters, derived from the leaves only, of these tliree species 

 of Ficiis are : 



F, benghalensis — Leaves elliptical-ovate, obtuse ; nerves 

 prominent beneath, distant, with intermediate reticulation, 

 the lower palmate. 



F. religiosa — Leaves broadly ovate, narrowed into a long 

 slender acumen, base narrowly cordate; nerves pinnate 

 from the base, scarcely prominent beneath, with intermediate 

 reticulation. 



F. elastica — Leaves oblong or elliptical, abruptly apiculate, 

 base entire ; lateral nerves obscure, pinnate from the base, 

 very numerous and closely parallel, without intermediate 

 reticulation in the lower part of their course. 



It will be observed that the diagnoses of species rest upon 

 comparatively slight modifications of structure. The dia- 

 gnoses of genera rest upon characters of higher importance 

 (characters more constant in the group than those used to 

 distinguish species), and so on for the groups superior to 

 the genus, the characters of each of which embrace, as we 

 have already shown, those of all their subordinates. The 

 method of denoting every plant and animal by two names, a 

 generic and specific, on a uniform plan, was invented by 

 Linnaeus, and this Binomial method is now universally 

 adopted by naturalists. 



The method of grouping genera into higher groups, ac- 

 cording to their resemblance in characters of successive 

 degrees of constancy, though indicated by the same eminent 

 man, has been the work of many collaborators, amongst 

 whom the names of Jussieu, Brown, and De Candolle are 

 pre-eminent. 



4. Precisely as we group species under Genera, so we 

 group genera under Natural Orders. The Natural Orders 



