FORM AND STRUCTURE 



they are wanting. The Sycamore and Black Willow afford 

 excellent examples of stipules. 



ARRANGEMENT. 



When leaves are distributed singly at different heights on 

 the stem, they are said to be alternate. When two stand op- 

 posite each other at the nodes, they are opposite. When 

 more than two are borne at a node in a circle around the 

 stem, they are whorled. 



KINDS OF LEAVES. 



Leaves are either simple or compound. 



A Simple Leaf has but one blade. The leaves of the Elm 

 are simple. A Compound Leaf has more than one blade ; 

 each blade is then called a leaflet. The leaves of the Sumach 

 are pinnately compound ; the leaves of the Horse-chestnut 

 are palmately compound. 



VERNATION OR PREFOLIATION. 



In the study of the leaves of trees considerable attention 

 is given to the way the leaves are folded in the bud ; this is 



Fic. 4. 



Fig. 5. 



Fig. 7. 



Fig. 9. 



called vernation. It may be studied from two points of 

 view ; how the leaves are arranged with reference to each 

 other, or how the individual leaf is folded. 



505 



