THE LEAF. 



27 



first foliage leaves may often be traced, as in the Lilac, 



Hickory, etc. When spines occupy the place of leaves, 



they are modified forms of the 



latter. In the Barberry all gra- 

 dations may be seen on a single 



shoot (Fig. 23). The leaf, or a 



portion of it, may become changed 



into a tendril for climbing, as in 



the Pea, Vetch, etc. (Fig. 24). 



28. Very interesting 

 modifications of leaves 

 are furnished by the 

 Pitcher-plant (Sarra- 

 cenia), Sundew (Dro- 



sera), and the Venus's Fly-trap {JDionfea). The 

 leaves of Sarracenia are hollow cups or tubes 

 (Fig. 25), covered within with hairs directed 

 downwards. They are generally half-full of a 

 liquid, into which insects may fall, and become 

 macerated, and their juices are then absorbed 

 by the plant. The 

 ^ Droseraisalsocar- ^^. _ v^"' 1 1 ' /','7 



nivorous, feeding on small 



insects which alight on and 



are held fast by viscid ten- 

 tacles or hairs on the upper 



side of the leaf. The leaves 



of Dioncea (Fig. 25a) have 



at the top two or three lobes 



furnished with a marginal 



Fig. 24. Tendril of the Pea-leaf. Fig. 25. Leaf, having the form of a pitcher, of 

 Sarracenia, or the Side-saddle Flower. Fig. 25a. Leaves of Venus's Fly-trap. 



