118 on varieties of domestic animals. Sept. 25+ 
we had seen no example, but much the reverse, had 
spontaneously separated, and in time become two dis- 
tinct fluids, both of which we are sure, inevitably to 
lose, if ever they fhall be suffered to mix together 
again? The production of distinct breeds of animals, 
is equally contradictory to the whole of the experi- 
ence we have had in the breeding of domestic ani- 
mals. It is easy for us when we please to adulte- 
rate any breed; bnt it totally exceeds onr power af- 
ter such adulteration to recover the pure breed a- 
gain. 
If, with a view to enlarge our ideas on this head, 
we go to vegetables, in regard to the varieties of 
which, philosophers entertain nearly the same opini- 
ons, we fhall find among those that are called varie- 
ties very great diversities, so as to constitute several 
distinct clafses. 
In one clafs, for example, among which may be 
ranked the common potatoe, we find that plants ob- 
tained from seeds are disposed to sport infinitely ; and 
none of the progeny can ever be expected to be found 
exactly of the same kind with the parent stock ; so 
that if that stock be not propagated otherwise than 
by seeds, it will be lost never to be recovered.* Ma- 
ny plants belong to this ciafs, as pinks, ‘carna- 
tions, &c. / 
Another clafs of plants, which are equally stiled 
warzeties are not liable to sport, or indeed to inter- 
mingle at all in breeding, but continue to propagate 
their own kind by seeds without variation. No 
i * See Bath society papers, vol. vi. 
