J.D. Hooker, Introductory Essay to the EJora of Tasmania. 17 
_* Mr. Darwin, after a very laborious analysis of many Floras, finds that the spe- 
cies of large genera are relatively more variable than those of small; a result whi 
was long disposed to doubt, because of the number of variable small genera an 
the fact that monotypic genera seldom have their variations recorded in systematic 
works, but an examination of his data and methods compels me to acquiesce in his 
statement. It has rem ry de Saint-Vincent, Voy. aux Quatre 
Iles de l'Afrique) that the species of islands ‘are more variable than those of con- 
tinents, an opinion I can scarcely subscribe to, and which is opposed to Mr. Dar- 
characterized iar genera, and 
are gen- 
by having few species in proportion to aa Bisexual trees and shrubs 
ya. : 
+ It should be borne in mind that the term natural, as applied to orders or other 
groups, has often a double significance; every natural order is so in the sense of 
members are so 1 con- 
that its differential characters can be expressed, and itself 
ie 
