LKSSON 7.] SPINES, TENDRILS, AND PITCHERS. 



51 



leaves is plainly shown, in many cases, by the gradual transition 

 between them and the first foliage of the shoot. The Common Lilac 

 and the Shell-bark Hickory are good instances 

 of the sort. But the best illustration is fur- 

 nished by the Low Sweet Buckeye of the 

 Southern States, which is often cultivated as 

 an ornamental shrub. From one and the same 

 growing bud we may often find all the grada- 

 tions which are shown in Fig. 77. 



123. leaves as Spines occur in several plants. 

 The most familiar instance is that of the Com- 

 mon Barberry. In almost any summer shoot, 

 most of the gradations may be seen between the 

 ordinary leaves, with sharp bristly teeth, and 

 leaves which are reduced to a branching spine 

 or thorn, as shown in Fig. 78. The fact that 

 the spines of the Barberry produce a leaf-bud 

 in their axil also proves them to be leaves. 



124. Leaves as Tendrils are to be seen in the 

 Pea and the Vetch (Fig. 20, 127), where the 

 upper part of each leaf becomes a tendril, which 



the plant uses to 



«Umb by ; and in ™ 



one kind of Vetch the whole leaf is 



such a tendril. 



125. leaves as Pitchers, or hollow tubes, 

 are famiUar to us in the common Pitcher- 

 plant or Side-saddle Flower (Sarracenia, 

 Fig. 79) of our bogs. These pitchers 

 are generally half-full of water, in which 

 flies and other insects are drowned, often 

 in such numbers as to make a rich 

 manure for the plant, no doubt ; though 

 we can hardly imagine this to be the 

 design of the pitcher. Nor do we per- 

 ceive here any need of a contrivance 

 to hold water, since the roots of these 

 plants are always well supplied by the wet bogs where they grow. 



FIG. 78. Summer shoot of Barberry, showing the transition of leaves into spines. 

 FIG. 79. Leaf of Sarracenia purpurea, entire, and another with the upper part cut off. 



