178 PRINCIPLES OF BOTANY, ETC. 
The form of the corolla is very various, as wé 
know from the Terminology: but there are many 
kinds of it that very nearly resemble one another. 
This great resemblance shews evidently that the 
transition from one to another is but small, and 
that nature does not guide herself according to our 
distinctions. A funnel-shaped corolla easily passes 
into a salver-shaped one, and vice versa; if genera 
were to be formed upon such small circumstances, 
the number would become too great. In the genus 
Convallaria, the species Solomon’s seal, (C. Poly- 
gonatum), has a tubular, the lily of the valley, 
(C. majalis), a bell-shaped corolla. Hence we see 
that these trivial variations of allied species of coa 
rolla are of little consequence. But when plants 
with monopetalous and polypetalous flowers are al- 
licd, they must form separate genera. ‘The form 
of the corolla must be very different when it gives 
occasion to form: new genera. 
§ 168. 
When the fruit in allied plants is very different, 
‘the genera must be separated. 
Plants may agree perfectly in their flowers while 
they bear’ very different fruit. If the variety in the 
fruit does not rest on the number of. the cells or of 
the seeds, or on the form of these alone, the plants 
must form distinct genera. ‘The example already 
brought from the genus Rhamnus, (§ 157), affords 
a proof of this. ‘The genera Abroma and ‘Theo- 
broma differ only in the fruit. Such distinctions are 
very beautiful, and ought never to be overlooked. 
4, § 169. 
