Introduction 



XIX 



depending upon whether the tree is growing in the open 

 or in a dense stand where it is shaded on the sides by its 

 neighbors. 



Leaves. Since leaves display characteristic patterns, they are 

 probably the most useful organs in identifying trees (Fig. 2). 

 Leaves consist of an expanded portion or blade, a supporting 

 stalk or petiole, and small leaflike or scaly structures {stipules) 



Fig. 4— TYPES OF INFLORESCENCES 



1-Ament. 2-Spike. 3-Raceme. 4-Panicle. 5-Umbel. 6-Corymb, 



attached in pairs at the base of the petiole. Leaves having no 

 stipules are termed exstipulate, and those without petioles are 

 called sessile. Those species which are evergreen can be identified 

 by their leaves throughout the year, while species which shed 

 their leaves annually (deciduous) must be identified by other 

 characters during the winter months. Leaves may be arranged 

 alternately (with one leaf attached to the twig at a certain point), 

 oppositely (where two leaves emerge at opposite sides from the 

 same place on a twig) whorled (where more than two leaves 

 emerge from one point of the twig), or fascicled (where a 

 number of leaves emerge in a cluster or bundle). They 

 may be simple and consist of a single blade or expanded 

 portion, or compound and made up of several individual 

 leaflets. If the leaflets in a compound leaf are arranged along 

 each side of a common axis (rachis), the leaf is said to be pinnately 

 compound, while if the leaflets all arise from the apex of 

 the petiole, the leaf is termed palmately compound. Other characters 

 used in identification are the shapes and types of margin, apex, 

 and base. Texture, color, and the surface, whether smooth or 

 hairy, are also useful characters. 



Flowers. All trees have flowers, although frequently they are 

 small and inconspicuous. These are the reproductive organs 



