ORGANS OF NUTRITIOX. 



Fig. 288. Fig. 289. 



151 



Fig. 288. Leaf of the Cherry with lamina, 

 petiole, and stipules. A large central 

 vein is seen to proceed from the petiole 

 to the apex of the leaf, and to give 

 off from its sides the otlier veins of the 

 leaf. This central vein is termed the 

 midrib. 



Fig. 289. Ribbed leaf of the Melon with a dentate margin. The venation is said 

 to be radiated or palmately veined. 



which are simply connected by unbranched veinlets (Jig. 290, b) ; 

 or it may divide at once into several veins or ribs, which 

 proceed from the base to the apex of the leaf, more or less 

 parallel to each 



other, and are in Fig. 290. 



like manner con- 

 nected only by 

 simple unbranched 

 veinlets {fig. 290, 

 a). The former are 

 called reticulated or 

 netted-veined leaves, 

 and occur almost 

 universally in Exo- 

 genous or Dicotyle- 

 donous Plants; the 

 latter are termed pa- 

 rallel-veined leaves, 

 and are character- ^^^- ^ 

 istic of Endogenous 

 or INIonocotyledo- 

 nous Plants. 



These two modifications are also subject to 

 others, a few of which we shall now notice. 

 l4 



^av. „. Parallel venation of a Grass : this va- 

 riety of venation is called straight-veined, b. A 

 variety of parallel venation termed curve-vemed 

 as seen in the Plantain. 



a variety of 



