6oo 



THE POPULAR SCIENCE MONTHLY. 



FIG. 5. BERBERIS AQUIFOLIUM. 

 branches. 



Leaves and 



the tree trunks, and finally gain support upon the branches of 

 the trees themselves. Unlike ordinary vines, however, which 

 only injure the plants that support them, the barberry may be 



of some service, as its arma- 

 ment of spines is well cal- 

 culated to repel intruders. 



The great aim of all this 

 spread and strengthening 

 of branch work is of coarse 

 to secure the most advan- 

 tageous exposure of foliage 

 to light ; to the attainment 

 of this object the form and 

 arrangement of the leaves 

 themselves also contribute 

 not a little. Wherever we 

 find such rosettes of wedge- 

 shaped leaves as the bar- 

 berry produces, the likeli- 

 hood of one leaf overshad- 

 owing its neighbor is much 

 reduced, and when as in 

 shady localities this matter 

 is of special importance, it is a noteworthy fact that the leaves 

 commonly adapt themselves to each other so perfectly that a 

 cluster becomes almost equivalent to a single large shield-shaped 

 blade. Moreover, on the more horizontal shoots the margins of 

 contiguous rosettes dovetail into each other so neatly that the 

 result may be justly compared to a mosaic of leaves. 



Another peculiarity connected with that abbreviation of the 

 branchlets which results in the rosette arrangement is the method 

 of defoliation. When the time arrives, the leaves, instead of sepa- 

 rating entirely, drop only the blade, while the flattened overlap- 

 ping leafstalks remain attached to the stem and perform the 

 function of bark for several years. 



It will thus be seen that we have in the barberry one of those 

 rare cases (paralleled by certain species of orange, grapevine, and 

 creeper) in which an apparently simple leaf has the blade ar- 

 ticulated with the stalk after the manner so characteristic of the 

 leaflets of compound leaves (Fig. 8). Of the hundred or more 

 known species of Berberis, about twenty (forming the subgenus 

 Mahonia) have compound leaves of from three to many leaflets 

 all plainly articulated at the base (Figs. 6 and 7), just as is also 

 the case with certain species of the genera Citrus and Vitis, to 

 which the orange and the grape respectively belong. Moreover, 

 throughout the Berberidacew we find almost all the species to pos- 



