As Fries has well remarked, little groups of species are generally clustered like satellites around other species.

And what are varieties but groups of forms, unequally related to each other, and clustered round certain forms--that is, round their parent-species.

Undoubtedly there is one most important point of difference between varieties and species, namely, that the amount of difference between varieties, when compared with each other or with their parent-species, is much less than that between the species of the same genus.

But when we come to discuss the principle, as I call it, of divergence of character, we shall see how this may be explained, and how the lesser differences between varieties tend to increase into the greater differences between species.
There is one other point which is worth notice.

Varieties generally have much restricted ranges.