sess leaves which are obviously compound, the chief exception being those eighty species (forming the subgenus Euberberis) which in their leaves agree essentially with Berberis vulgaris. In view of these facts, botanists have been led to adopt the somewhat paradoxical theory that leaves of the euberberis type are in reality compound though unifoliolate.
The question as to how such a curious state of things could have come about is so closely connected with what concerns the evolution of the other vegetative organs that we shall do well to consider them all together.
In attempting to reconstruct for ourselves the main features of the original ancestral barberry we are much helped by the fact that besides Berberis vulgaris, which is the only representative of the genus in central Europe, there have been developed a multitude of species in Asia and a still larger number in the two Americas; for it is clear that this must considerably increase the chances of our being able to find something like the primitive form persisting in certain living species. Guided by the principle that evolution is for the most part attended by increase of differentiation,
|Fig. 6.||Fig. 7.||Fig. 8.|
|Fig. 6.—Berberis aquifolium. Quinquifoliolate leaf.|
|Fig. 7.—Berberis trifoliata. Trifoliolate leaf.|
|Fig. 8.—Berberis vulgaris. Unifoliolate leaf. A indicates the point of articulation of the leaflet.|
we may fairly assume that the branch system of the prototype differed from Berberis vulgaris in having the internodes approximately equal, thus making the lateral branches on the one hand and the main branches on the other more nearly of a length and all the leaves uniformly disposed in elongated spirals.
Such a condition is indeed tolerably well exhibited in the mahonias, as may be seen in the "holly-leaved barberry" (Fig. 5),