PRELIMINARY TREATISE. 
19 
the irrefragable test of facts, which are daily becoming more 
notorious ; and we cannot proceed a step without flounder- 
ing into inconsistencies, unless we take the generic characters 
to be the definitions of identity of kind, and in strict agree- 
ment with that, they must, where it shall appear necessary, 
be carefully reformed. Jussieu has stated, in the perspicuous 
Latin Introduction to his History of Plants, that the founda- 
tion of botanical science rests on the distinction of species, 
which he defines to be a perennial succession of like indi- 
viduals renewed by continual generations, and adds that 
although they may be sometimes a little diversified by 
climate, disease, or culture, the seminal produce will return 
to the original type. He then considers the union of species 
in genera to be a discretionary work for the assistance of the 
memory, attempted at first without rule, and latterly con- 
structed with more propriety by reference to the fructifica- 
tion. Upon the same premises I should have come to the 
same conclusion ; but that statement is contradicted by the 
complete confusion of vegetable species which may be pro- 
duced by reciprocal intermixture ; and horticultural expe- 
riments have established, beyond the possibility of refutation, 
that botanical species are only a higher and more permanent 
class of varieties ; and that even the local and cultivated 
varieties to which he alludes, if they do not come iu contact 
Avith other varieties, instead of reverting, as he supposed, to 
an original type, are renewed with considerable uniformity 
in their generations. It is now certain that individuality 
does not, as Jussieu had imagined, coincide with the species 
of botanists, but with a higher and more comprehensive 
grade, which seems to accord with such genera as are truly 
defined, and would agree with all if properly reformed ; and 
if he had known, what our later experiments have established, 
his logical mind would certainly have assented to my pro- 
position, which is in truth but the application of his own 
doctrine to facts which have since come to light. The labours 
of the many distinguished cultivators of the science have been 
daily tending to place the genera on a correct footing, but it 
will never be perfectly accomplished till the erroneous notion 
of the original diversity of all vegetable species is thoroughly 
discarded. If the original ' constructors of the system had 
known all that is at present ascertained, they would perhaps 
have called the botanical genera species, and the species 
varieties ; but it does not appear to me advisable at present 
c 2 
