THE STRUCTURE OF LEAVES 



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FIG. 312. The life of this elm was preserved (4) by removing the 

 decayed part, and CB) by filling the cavity with cement. 



in your city, do what you can to keep the trees in a healthy 

 condition. 



The structure of leaves. A leaf usually consists of a broad 

 flat part, called the blade, and of a stalk, called the petiole. 

 Sometimes the petiole is missing and the leaf is attached directly 

 to the plant stem. The blade may be of any shape : in grass it 

 is long and very narrow; in nasturtium it is almost circular; in 



FIG. 313. The shape of leaves varies. 



poplar leaves it is almost heart-shaped (Fig. 313). Sometimes 

 the blade is indented as in maple leaves ; sometimes it is divided 

 up into a number of distinct leaflets as in the rose and horse- 

 chestnuts (Fig. 314). Through the blades of all leaves, no 

 matter what their shape, run numerous conspicuous veins. 



