120 On the requisites necessary 
ia the elaboration of the genus. So clear is my opinion upon this 
point, that, if it had been possible to prove the four species to which 
I have alluded to be themselves physiologically distinct, I should at 
once have reduced all the others to their original places ; but as it 
is in the highest degree uncertain whether R.fruticosus, corylifo- 
lius and ccesius are not as much varieties of each other, as those 
which it would be necessary to reject, I have thought it bet- 
ter to steer a middle course, until some proof shall have been ob- 
tained either one way or the other. Accordingly, I have taken R. 
Jruticosus, corylifolius , ccesius ami suberectus as heads of sections, 
and I have assigned them characters which may be considered either , 
as sectional or specific, according as the evidence may ultimately 
preponderate ; and I have arranged as species under them those 
forms which are the best marked and the most clearly distinguish- 
able. This will bring the genus Rubus somewhat into the situation 
of Rosa ; in which, I fear, we must -be satisfied with leaving it for 
the present." 
We have dwelt somewhat longer upon this topic than to many 
may seem advisable, but we feel so thoroughly persuaded of the very 
great importance of some exertions being made for the purpose of 
obtaining a better criterion for the descrimination of species than 
the mere empirical rules at present practised, that we trust to be 
excused for attempting to direct the attention of all those who have 
it in their power to follow up the subject experimentally, to this 
very desirable object. 
Although we must not hope to attain that degree of perfection in 
systematic botany, which would probably be the immediate result 
of our detecting the laws which regulate the limitation of species ; 
yet much has been, and much more may unquestionably be achiev- 
ed, through the means actually in our power, towards distributing 
plants into natural groups, and pointing out the relations which such 
groups bear to each other. Nothing has of late years contributed so 
much to the progress of systematic botany, as the publication of se- 
parate monographs of genera, tribes, and orders by different indivi- 
duals. The number of species already known is so great, that no 
single botanist can ever hope to examine in minute detail more than 
a small fraction of them. He may, however, become thoroughly ac- 
quainted with the leading characteristics of every order, and of their 
subordinate groups, and many of their genera, by merely examining 
for himself a portion of the species which they each include. But 
if, in addition to his general studies, he also directs his attention more 
especially to some particular group, for the purpose of completely 
