De Candolle then goes on to say that he gives the rank of species to the forms that differ by characters never varying on the same tree, and never found connected by intermediate states.

After this discussion, the result of so much labour, he emphatically remarks: "They are mistaken, who repeat that the greater part of our species are clearly limited, and that the doubtful species are in a feeble minority.

This seemed to be true, so long as a genus was imperfectly known, and its species were founded upon a few specimens, that is to say, were provisional.

Just as we come to know them better, intermediate forms flow in, and doubts as to specific limits augment.

" He also adds that it is the best known species which present the greatest number of spontaneous varieties and sub-varieties.