172 PRINCIPLES OF BOTANY, ETC. 
of a firm substance. In like manner in Daphne 
Mezercum there is but one part, which is coloured, 
much longer than the stamina but of a firm sub- 
stance. ‘There are some allied genera that have yet 
a smaller calyx; even some species of Daphne that 
have something like a calyx ; ; and therefore this part : 
in the Mezereum must be called a corolla. But 
besides” the three characters given above, we ought 
fo attend to the affinity with, other plants, and we 
will seldom err. 
§ 157. 
In constructing new genera, it is necessary, ¢hat 
ihe essential character be applicable to all the species 
of the genus, and be subject to no variation. 
As the flower and fruit of one species are formed, 
so must those of all the rest be. For example, the 
fruit of one cannot be a berry and of another a 
drupa, though Linné has committed this mistake in 
the genus Rhamnus, which properly makes two dis. 
tinct genera, namely, Rhamnus and Zizyphus. 
§ 158. 
the character of a genus must be formed from the 
number, figures situation and proportion, (S 157), of 
the flower and frit. 
It is only these circumstances, taken together, that 
constitute genera; taken separately, they are of no 
consequence. There are often species, which de- | 
viate from the generic character in this or that par- 
ticular; but on that account they are not to be con- 
sic lered as distinct genera. 
