120 



PLANT LIFE. 



attached, i.e., it is bilateral. Moreover, the upper and under 



surfaces are usually different, i.e., it 



is dorsiventral. It has three parts, 



the base, the stalk, the blade (fig. 



136). The leaf base is always 



present, but either the leaf stalk or 



the leaf blade or both may be absent. 



The leaf blade is ordinarily winged ; 



indeed it is for this reason that it 



Fig. 136. Fig. 137. 



Fig. 136. — Leaf of Ranunculus Ficaria. />, leaf base; /, petiole, or leaf stalk; /, 



lamina or leaf blade. Natural size. — After Prantl. 

 Fig. 137. — A leaf of a grass, with part of stem to which it is attached, s, sheath (leaf 



base) attached all around node k of the stem h, h ; /, blade ; /, the ligule, an outgrowth 



from the surface. Natural size. — After Frank. 



received the name " blade." Either the stalk or the base or 

 both may also be winged. 



151. 1. The leaf base. — The leaf base is generally en- 

 larged so as to form a sort of cushion by which it is attached 

 to the stem. t When a broad base is attached over a consider- 

 able arc of the circumference of the stem, so that it encircles 

 it more or less, the base is said to be sheathing (fig. 136). 

 In grasses, for example, the leaf base is attached over the 

 entire circumference of the stem, and enwraps it completely 

 for a considerable distance above the node (fig. 137). 



