ON THE DISTINCTION OF SPECIES. 617 
Secondly, let it be found impossible to convert one form 
into the other, merely by change of external circumstances 
affecting the individual plants, but that one of them will re- 
appear in plants raised from seeds of the other, either in the 
first descent or in any future progeny. Here, again, all 
botanists would consent to unite both forms under one spe- 
cific name, no matter how wide their differences might be. It 
is said that Anagallis arvensis has been raised from seeds of 
Anagallis cerulea ; also, that Primula vulgaris has been raised 
from seeds of Primula veris. If there be no mistake in 
the facts, these couplets of alleged species clearly constitute 
only single real species. It is seldom, however, that well- 
marked varieties can be thus converted in a single descent: 
more commonly the change is gradual, and fully completed 
only after numerous descents, each in turn becoming less 
and less like the original plant or variety from which they 
are descended. Our garden vegetables show this forcibly ; 
fora gardener never expects to see the wild stocks when he 
sows varieties of the cabbage, lettuce, pea, carrot, &c. Yet, 
very commonly, some few plants in the seed-beds of a garden 
may be found retrograding towards the typical or wild form ; 
and if these be not thrown out, the race or variety quickly 
deteriorates. . 
Unfortunately, the satisfactory tests of direct metamor- 
phose and conversion through seed, are very seldom brought 
to bear upon the determination of species, even in those cases 
where the tests might be applied with ease and certainty ; 
and, in a vast many instances, it is impossible to apply them. 
Systematic botanists are, therefore, usually content to adopt 
as distinct species, all those forms which present some marked 
peculiarities, by which, as it is supposed, they can certainly 
and always be distinguished from each other. But it has, 
from time to time, been shown, that several of the supposed 
species, so described, were not permanently distinct from 
each other; while a still larger number of them may be said 
to be under suspicion. This leads to the necessity of dis- 
tinguishing two kinds of species ; namely, those forms which 
