74 ^^A VES. [CHAP. 



from shortened branches is obvious on examination, for 

 they occupy the axils of the smaller scale-leaves, and some 

 of them occasionally develope their internodes, when, con- 

 quently, the needle-leaves are borne singly upon the shoot, 

 and are separated from each other by more or less marked 

 internodes. 



5. The cotyledons are the first leaves of the primary 

 axis of the plant. They are usually, but not always, very 

 shortlived, and shrivel up and die at an early stage. In 

 some plants they never leave the testa of the seed, but 

 remain underground, while in others they rise above the 

 surface and assume partially the functions of ordinary 

 foliage-leaves. The first leaves of branches ordinarily diff"er 

 from those which follow, in being much smaller, and often, 

 in certain Natural Orders and in cool climates, in being hard 

 and scaly. These are the scale-leaves. They serve as pro- 

 tective organs to the delicate rudiments of the foliage-leaves 

 which they enclose, and into which they usually pass more 

 or less gradually, thus convincingly showing that they are 

 both modifications of one and the same organ. 



Many trees develope each season terminal as well as 

 axillary buds. As before pointed out, it is only by the 

 development of the former that the original stem or its 

 branches are prolonged. Some plants never renew their 

 branches by annual terminal buds, while others annually 

 develope branches from both terminal and axillary buds. 

 This variety of conditions in respect to the relations of 

 terminal and axillary buds has much to do with the 

 general aspect of the tree. 



Leaves vary in their duration. * They may last but one 

 season, at the close either separating by an articulation from 

 the stem, leaving a clean scar, or remaining attached and 

 gradually decaying. In Evergreens, the leaves last two or 



