VENATION OR NERVATURE 



185 



The forms all fall within two principal classes, which, in general, 

 characterize respectively the monocotyledons and the dicotyledons. 

 The former hears its ])rincipal veins more or less ])arallel with one 

 another, and these are munerons. Snch lea\es are called I'andlcl- 

 veined (Fig. 52G). 



Venation or Ncrvature: Fig. 524. Pinnateiy veined leaf of Castanea: a, midrib; b, secondaries; c, 

 tertiaries. 525. Reticulate leaflet of Pilocarpus: a, anastomosis of secondaries. 526. Parallel-veined 

 leaf of Convallaria. 527. Flabellately costate leaf of Plantago. 528. Digitately veined leaf of Cercis. 

 529. Costinerved leaf. 



In the second form there is hut one, or a comparati\'ely few t)ri<,nnal 

 veins, and these give rise to successively developed branch systems, 

 the whole forming a network or Reticulum. Such leaves are called 

 reticulated or Xetted-veined (Fig. 524, etc.). These veins may or may 

 not anastomose or intercommunicate at their distal ends. When they 



