BARBERRIES. 



605 



undershrubs in our Western States, as well as other apparent 

 exceptions among Berberides to the general principle we are now 

 applying. 



Along with the firm texture "belonging to evergreen leaves 

 there would naturally be retained the marginal spines which pro- 

 tected the mahonia ancestors from browsing animals. But with 

 the establishment of the rosette arrangement the leaves which 

 are borne by a long shoot, in virtue of their position just below 

 the rosettes, come to have a special importance in this protective 

 capacity. For, in the first place, as being already fully developed 

 at a time when the rosette leaves are young and 

 tender, the old leaves can shield the newer ones 

 at the most critical period of their life ; and, in 

 the second place, given one stout, spiny leaf in 

 such intimate connection with the mature clus- 

 ter, and the need for using up material in spine- 

 making for the latter is much lessened. Ac- 

 cordingly, we find very generally throughout 

 the evergreen Eiiberberides, along with the dif- 

 ferentiation of the branches into long and short, 

 a differentiation. of the leaves those subtend- 

 ing the clusters being decidedly spiny, while 

 those of the cluster are less strongly armed. A 

 particularly good example of such differentia- 

 tion not far advanced is afforded by a species 

 growing in Chili (Fig. 9). In a number of cases, 

 such as the "box-leaved barberry" (Berberis 

 buxifolia, Fig. 10), the differentiation has been 

 carried so far that the subtending leaf has been 

 completely transformed into a formidable spine, 

 while the rosette leaves have lost all trace of spines except at 

 the tip. 



After the plurifoliolate and the unifoliolate types of evergreen 

 barberries had been evolved there was the further possibility of 

 developing from the latter a yet higher type which should be still 

 better adapted to meet the exigencies of a severe and snowy win- 

 ter, and at the same time safely attain a considerable height. All 

 this would follow from the acquirement of the deciduous habit. 



In the series of forms which came to adopt the expedient of 

 defoliation at the approach of winter, several causes may have 

 conspired to bring about in the two sorts of leaves a still further 

 specialization of the two functions of assimilation and defense, 

 which, originally combined in each leaf, began, as we have seen, 

 to be separated more or less in the evergreen Euberberides. 



As regards the subtending leaves, not only would their impor- 

 tance as a defense to the young rosette be sufficient to insure their 



FIG. 9. BERBERIS TO- 

 MKNTOSA(?). Leaf 

 rosettes subtended 

 by stouter spiny 

 leaves. 



