LEAVES AS SPINES 173 



animals in very much the same way as is ZIZYPHUS. 

 But the curved thorns also assist in climbing, for by 

 them, the branches catch in the back of other trees 

 and are prevented from slipping back. 



We should notice too that in this plant, there are 

 three or four flower buds in the axils of some of the 

 leaves, and that these buds are one above the other, 

 in a vertical line, the oldest (the first flower to open) 

 being at the top (fig. 18, p. 95). 



BERBERIS ARISTATA, D.C. 



The common Barberry of the hills. 



This is a very common plant growing wild on the 

 hills. The branches are armed with sharp slender 

 spines, which are generally three-pronged. Just above 

 each three-pronged spine is a very short branch covered 

 with small scales, and ending in a tuft of leaves, 

 or perhaps a bunch of flowers. 



The three-pronged spine may represent one of two 

 things it may be a branch or a leaf. If it is a 

 branch there must be below it a subtending leaf 

 (or the scar of one), and the total absence of any sign 

 of one shows that the spine is homologous with a 

 leaf. The short branch above it is its axillary 

 branch, the first few leaves of this are modified as 

 small scales, and are followed by the normal leaves. 

 Even if it bears flowers, this axillary branch is a 

 short one of limited growth for the flowers termi- 

 nate it. 



One effect of the spines is clearly to prevent ani- 

 mals eating the plant and the three-prongs are, for 

 this of course, better than one. The leaves are all 



