LEAVES 



19 



of two-ranked alternate leaves, while the Apple leaves 

 are alternate without being two-ranked. Most leaves 

 spread from the stem, but some are appressed, as in the 

 Arbor-vitae (Fig. 7). In this spe- 

 cies the branches are two-ranked. 



PARTS OF LEAVES. A complete 

 leaf^^^ consists of three parts : 

 the blade, the thin expanded por- 

 tion ; the petiole, the leafstalk ; 

 and the stipules, a pair of small 

 blades at the base of the petiole. 

 The petiole is often very short 

 and sometimes wanting. The Fig. 7. 



stipules are often absent, and, even when present, they 

 frequently fall off as soon as the leaves expand; some- 

 times they are conspicuous. Most Willows show the 

 stipules on the young luxuriant growths. 



VEILING. The leaves of most 

 trees have a distinct framework, 

 the central line of which is called 

 a midrib ; sometimes the leaf has 

 several other lines about as thick 

 as the midrib, which are called 

 ribs ; the lines next in size, includ- 

 ing all that are especially distinct, 

 are called veins, the most minute 

 ones being called veinlets (Fig. 8). 



KINDS. Leaves are simple when they have but one 

 blade ; ~{fjjfjj^\compound when they have more than one. 

 Compound leaves are palmate when all the blades come 

 from one point, as in the Horse-chestnut ; Mjjg& and pin- 

 nate when they are arranged along the*"""*!^ sides, as 

 in the Hickory. Pinnate leaves are of two kinds : odd- 



