18 
PRELIMINARY TREATISE. 
and I apprehend that the distinction of vegetable species is 
mainly referable to a period as early, and was consequent on 
the dispersion of seeds into different climates by the operation 
of the deluge. Looking to the multitude of forms which the 
several kinds or genera have assumed, it becomes a matter 
of considerable difficulty, and requires much discernment, to 
ascertain which are the features that may be relied upon as 
indicating an absolute and original diversity. The specific 
differences in one kind may embrace a wide range ; the 
actual difference between another kind and those most nearly 
resembling it may be very small. The feature which is 
symptomatic of individuality in one family of kindred plants, 
may not be so in another ; such as the absence or presence 
of a tube or any particular appendage. In forming generic 
characters we are but seeking signs whereby to come at the 
knowledge of a fact, namely, the individuality of a thing 
described. For the purpose of assisting our view of nature, 
we arrange them in groups, to which however no distinct 
limits were assigned by the Creator; and, though w r e are 
trying to find out the ways of nature, our classifications, by 
whatever name we may call them, are artificial, and if we 
proceed beyond one step at a time, we must be liable to find 
ourselves baffled by the reality. When I began, many years 
ago, to write concerning vegetables, I had to combat an idea 
that the Almighty had created each species of our botanical 
catalogues as it now exists, and that plants being able to 
breed together was the test of their identity as species. It 
has since been ascertained beyond dispute, as I then antici- 
pated, that in some genera all the species are capable of easy 
intermixture ; and that even some, which botanists had 
erroneously placed in different genera,* could produce a fer- 
tile cross-breed. It cannot be asserted on the other hand that 
such are merely instances of erroneous multiplication of 
species by botanists, because they include almo^ every sort 
of diversity which, when found among spontaneous vege- 
tables, have generally been taken as specific characteristics, 
and the facility of intermixture seems to depend less on the 
botanical than the constitutional affinity of kindred species ; 
so that either the whole existing machinery of species must 
be upheld, or they must fall together. The opinion, which 
I had at first to combat, is therefore falling to the ground by 
* For instance, Crinum and Amaryllis. 
