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. Unfortunately historical evidence on this point is almost wholly lacking. The differences in question could not have been appreciated at that remote period, and interest the common observer but little even today. The history of most of the cultivated plants is very obscure, [66] and even the most skillful historians, by sifting the evidence afforded by the older writers, and that obtained by comparative linguistic investigations have been able to do little more than frame the most general outline of the cultural history of the most common and most widely used plants. Some authors assume that cultivation itself might have been the principal cause of variability, but it is not proved, nor even probable, that cultivated plants are intrinsically more variable than their wild prototypes. Appearances in this case are very deceptive. Of course widely distributed plants are as a rule richer in subspecies than forms with limited distribution, and the former must have had a better chance to be taken into cultivation than the latter. In many cases, especially with the more recent cultivated species, man has deliberately chosen variable forms, because of their greater promise. Thirdly, wide variability is the most efficient means of acclimatization, and only species with many elementary units would have offered the adequate material for introduction into new countries. From this discussion it would seem that it is more reasonable to assert that variability is one of the causes of the success of cultivation, than to assume that cultivation is a cause of variability [67] at large. And this assumption would be equally sufficient to explain the existing conditions among cultivated plants.