I20 



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 ahva)'S 



present, but either the leaf stalk or 



the leaf blade or both maybe absent. 



The leaf blade is ordinarily winged ; 



indeed it is for this reason that it 



" I 



Fig. 136. IiG. 137. 



Fn; 136. — Leaf ci Kanmiciilus Ficarhi. /■, leaf tiase; /, petiole, or leaf stalk; /, 



laniina or leaf blade. Natural size. — After IVantl. 

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



l:)ase) attached all around node k of the stem //, /; ; J\ blade ; /, the Kgule, 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. I. 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. When a broad base is attached over a consider- 

 able arc of the cin.uniference of the stem, so that it encircles 

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

 In grasses, for e,\ample, the leaf base is attached o\cr the 

 entire circumference of the stem, and enwraps it com])letely 

 fof a considerable dislaiicc abrn-e the node (fig. 137). 



