LEAVES. 57 



still further and form the tripinnate leaf, as in the Thalictrum 

 (Fig. 87), and it even exceeds this subdivision when the terra 

 supra-decompound is applied to them, no matter how far the 

 divisions may extend. When the midrib is terminated by a 

 leaflet, the leaf is said to be unequally pinnate. (Fig. 88.) 



95. The radiated form of reticulated leaves often assumes the 

 compound structure, as in the ^sculus, Lupinus, Clover, <fec. 

 (Fig. 63), and are then called digitate. If there are three leaf 



Fig. 90. 



Ternate leaf. 



lets, it is called a ternate leaf. (Fig. 90.) If subdivided by 

 three, they are bi-ternate, tri-ternate, &c. (Fig. 91.) 



96. Besides the preceding varieties of leaves, which may be 

 considered their common forms, they often assume a variety of 

 modifications which deserve a special attention. These varia- 

 tions arise from a variety of causes, which will be noticed under 

 the several examples which we shall adduce. A cohesion of 



Fig. 91. 



Biternate leaf. 



parts not unfrequently creates a variation from the usual form. 

 When two leaves unite by their bases, they are connate. When 

 leaves adhere to the stem, forming a kind of wing beneath, 

 then they are said to be decurrent. The bases of the upper 

 leaves of the Caprifolium sempervirens are brought in contact 

 from the unusual development of both systems of the leaf, and 

 they grow together, forming a perfoliate leaf. The same takes 



When tripinnate ? If farther divided, what are they called ? What i* 

 an unequally pinnate leaf ? — 95. What is a digitate leaf? When called 

 ternate ? Bi-ternate ? Tri-ternatc ? — 96. When are leaves said to be con- 

 nate? When decurrent? W1>cb perfoliate ? 



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