Page:Popular Science Monthly Volume 45.djvu/622

602 which is a fair example of the Mahonia group. At the same time it is worthy of note that along with the greater uniformity of the branches is associated the possession of compound leaves having from three to many leaflets. This fact, taken in connection with the circumstance that almost all the other members of the family have the leaves more or less plainly of the palmate type, makes it probable that the ancestor of the barberries had trifoliolate leaves not unlike those often found interspersed among the larger leaves of the multifoliate mahonias and appearing also as the sole form on other species of the same subgenus (compare Figs. 5 and 7). It is significant, moreover, that the mahonias are without the highly developed spines so characteristic of the Euberberides, but depend for protection upon the spiny margins of their evergreen leaflets.

Thus, whether we consider the approach toward similarity among the branches, the approximation in the type of leaf to that most common in the family, or the absence of specialized spines, we are led to the conclusion that the Mahoniæ since they exhibit so much less differentiation than the Euberberides, must therefore represent more nearly the primitive features of the genus—a conclusion which is confirmed by such paleontological evidence as we possess. For the five species discovered in the Tertiary formation of southern France, northern Italy, and Switzerland are all mahonias, one of them (Berberis helvetica) closely resembling the American holly-leaved mahonia here figured, while others are like forms living at present in China. In view of these facts we shall probably be not far from the truth if we picture to ourselves the ancestral Berberis as being a small bush or underbrush resembling in a general way our evergreen holly, but having in place of each simple leaf a compound one of three leaflets. Almost exactly corresponding to this description is the already mentioned Berberis (Mahonia) trifoliata of Mexico and the adjacent regions.

That the ancestral home of the barberries was most probably in the northern part of North America appears from what is known of the geographical distribution of the species when viewed in the light of the generalizations arrived at by Bentham, Hooker, and Asa Gray regarding the origination of the members of the north temperate flora. We learn from Bentham that "to the great majority of them no primeval antiquity can be ascribed in central or western Europe; they appear to have come from the East, a considerable number perhaps from western Asia, where their types appear to be more varied, but many also must have made half the tour of the globe. Large American genera have sent out offsets into eastern Asia, which, gradually diminishing in number of species and sometimes slightly modifying their character, have