290 VEGETABLE ORGANOGRAPHY. 



manner two united leaves, vv^hich enclose the following 

 shoot. 



The leaves may also be adherent to the stem, after 

 two systems, confounded in books under the name of 

 Decurrent leaves : we call by this name all those the 

 limbs of which are prolonged on both sides into foliaceous 

 tongues, which seem to arise from the stem. This appear- 

 ance may be produced by two causes : — 



1st. The leaf may be adherent to the stem by the 

 upper surface of its middle nerve, so that it seems to 

 proceed from the stem at the place where its junction 

 with it ceases, and the part of its limb which arises from 

 the portion of the nerve adherent to the stem seems to 

 proceed from the stem itself, and form two lateral wings. 

 This takes place in the floral leaf of the Lime (Tilia), 

 and in the leaves of several species of Solanum. 



2d. The leaf may be prolonged at its base into 

 auricles, which are directed along the stem, and are 

 adherent to it : this happens in most of the leaves said 

 to be decurrent. Prenanthes viyninea presents a very 

 remarkable example. 



Leaves can, as we have said, be united to peduncles, 

 which thus seem to spring from the petiole or the leaf; 

 but as this phenomenon has more importance in the 

 history of the peduncle than in that of the leaf, we shall 

 speak of it when we treat of the Inflorescence. 



There are cases where the distinction between leaves 

 and peduncles, which appears clear and easy in general, 

 becomes extremely complicated ; this happens in the 

 Ferns. 1 have purposely omitted mentioning them in 

 this chapter on Leaves, for the organs called leaves may 

 indifferently be considered either as true leaves, which 

 bear the flowers and fruit, or as peduncles, bordered by 

 foliaceous wings ; under this doubt I shall delay treating 

 of them until I speak of the fructification of this family. 



