Recalling the results of the last lecture, we see that the species of the systematists are not in reality units, though in the ordinary course of floristic studies they may, as a rule, seem to be so. In some cases representatives of the same species from different countries or regions, when compared with one another do not exactly agree. Many species of ferns afford instances of this rule, and Lindley and other great systematists have frequently been puzzled by the wide range of differences between the individuals of a single species.

In other cases the differing forms are observed to grow near each other, sometimes in neighboring provinces, sometimes in the same locality, growing and flowering in mixtures of two or three or even more elementary types. The violets exhibit widespread ancient types, from which the local species may be taken to have arisen. The common ancestors of the Whitlow-grasses are probably not to be found [64] among existing forms, but numerous types are crowded together in the southern part of central Europe and more thinly scattered elsewhere, even as far as western Asia. There can be little doubt that their common origin is to be sought in the center of their geographic distribution.

Numerous other cases exhibit smaller numbers of elementary units within a systematic species; in fact purely uniform species seem to be relatively rare. But with small numbers there are of course no indications to be expected concerning their common origin or the starting point of their distribution.

It is manifest that these experiences with wild species must find a parallel among cultivated plants. Of course cultivated plants were originally wild and must have come under the general law. Hence we may conclude that when first observed and taken up by man, they must already have consisted of sundry elementary subspecies. And we may confidently assert that some must have been rich and others poor in such types.

Granting this state of things as the only probable one, we can easily imagine what must have been the consequences. If a wild species had been taken into cultivation only once, the cultivated form would have been a single elementary [65] type. But it is not very likely that such partiality would occur often. The conception that different tribes at different times and in distant countries would have used the wild plants of their native regions seems far more natural than that all should have obtained plants for cultivation from the same source or locality. If this theory may be relied upon, the origin of many of the more widely cultivated agricultural plants must have been multiple, and the number of the original elementary species of the cultivated types must have been so much the larger, the more widely distributed and variable the plants under consideration were before the first period of cultivation.

Further it would seem only natural to explain the wide variability of many of our larger agricultural and horticultural stocks by such an incipient multiformity of the species themselves. Through commercial intercourse the various types might have become mixed so as to make it quite impossible to point out the native localities for each of them.