172 



ORGANOGRAPHY. 



Epimedium, it is triternate or triply ternate (fig. 348); when 

 such a leaf is still further divided, it is said to be decompound. 



y^^ 



Fig. 348. Triternate leaf of Bane-berry {Actcea). 



5. PETIOLE OR LEAF-STALK. 



The petiole or leaf-stalk is that part which connects the 

 blade of tlie leaf with the stem (figs. 284 and 349). It is 

 frequently absent, and the leaf is tlien said to be sessile (fig. 263). 

 It consists of one or more vascnlar bundles, surrounded by 

 parenchyma (fig. 349,/y, pc), and tlic wliole is enclosed in a 

 layer of ci)idcrmis, wliich contahis but few, or no stomata. 

 The vascuhvr bundles vary in tlieir nature in the leaves of the 

 different classes of plants, being- merely prolongations of those 

 of the three kinds of stem already fiilly described ; thus, in 

 Dicotyledonous Tlants, the vascular bundles which proceed from 

 the interior of the stem, as shown in fig. 284, consist of spiral, 

 ])itted, and laticiferous vessels, and wood-cells, or of the same 

 elements essentially, as the wood itself. The ramification of the 



