in Natural History. 483 
can communicate. to his neighbour his perception of their dif- 
ferences. ‘Thus botanists speak of certain species of plants dif- 
fering in appearance, habit, touch, &c.; by which they often 
mean that they have some indescribable peculiarities about them, 
which point them out to the practised observer as distinct. A 
great number of such species may be detected in every modern 
Flora of a well investigated country ; but whether they deserve 
to be ranked among those which are capable of definition, is a 
question of great doubt :—that the practice is an inconvenience, 
none will deny ; and if it be much longer continued, will involve 
in inextricable difficulty all our well known species, make us 
dependent upon empirical and traditional evidence for our ac- 
quaintance with them, and render it impossible to derive instruc- 
tion from books. In such cases the assumed law ought to be 
broughtto the test of experiment, or the speciesshould be rejected. 
Many of our cultivated plants also tend to invalidate the law. 
Who can refer our cerealia and esculent vegetables, in many 
instances, to their true types? and how few of our old flowers 
are there, of which the astutest botanist can trace the origin! 
Domesticated animals afford a still more striking example; 
and man himself furnishes the most difficult problem of all. 
These remarks and examples are, I apprehend, sufficient to 
show how difficult itis to adopt the term in its strict acceptation ; 
and that however precisely the naturalist has attempted to em- 
ploy it, he has not succeeded to the extent he has proposed; and 
that it can only be taken as correct in a vague and general sense, 
and as a convenient abstraction to relieve him at the first step 
from the necessity of becoming acquainted with every individual. 
The next term of importance to the naturalist upon which the 
accuracy of his reasoning depends, is that division of his system 
which he denominates a Genus. This is an assemblage of in- 
dividuals agreeing also in some common characters ; but, unlike 
the 
