THE LEAF. 



31 



(Fig. 34), If the leaf is folded like a fan (e.g. Maple) it 

 is said to be plicate, or plaited. It is circinate (e.g. 

 Ferns) when 

 rolled from the 

 tip downwards 

 (Fig. 35); con- 

 volute (e.g. 

 Plum) when 

 rolled from one edge into a coil (Fig. 36) ; when rolled 

 from both edges inwards (e.g. Violet) it is involute (Fig. 

 37) ; when rolled outwards (e.g. Azalea) it is revolute 

 (Fig. 38). 



34. A leaf may have three parts, namely : the blade, 

 or lamina, which is the expanded portion (Fig. 39, hi); 

 the petiole (Fig. 39, pet), which is the stem of the leaf; 

 and stipules, which are the appendages at the base of the 

 petiole (Fig. 39, stip). The stipules are very often want- 

 ing, in which case the leaf is said to be exstipulate. If 

 the blade is inserted directly on the stem 

 (which is the case when the petiole is absent), 

 the leaf is said to be sessile. The blade 

 consists of a net-work of veins or skeleton 

 . of woody tissue, and the soft, green tissue 

 -Ji. between the veins called parenchyma (Gr. 

 para, by; enchein, to fill in). When one 

 vein surpasses the others in size it is called 

 the midrib (Fig. 39, m.r.) ; its branches are 

 the veins (Fig. 39, vn), and the branches 

 from the veins are the veinlets (Fig. 39, vnl). 

 35. If the venation of a large number 



Figs. 34-38. Vernation: 34. Conduplicate ; 35. Circinate; 36. Convolute; 37. 

 Involute; 38. Revolute. Fig. 39. A leaf: 6i, blade; ^^/, petiole; siip, stipules; 

 m,r., midrib ; vn, veins ; vnl, veinlets ; tff, apex. 



vn. 



JjUI> 



