VENATION OR NBRVATVRE 



185 



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

 characterize respectively the monocotyledons and the dicotyledons. 

 The former bears its principal veins more or less parallel with one 

 another, and these are numerous. Such leaves are called Parallel- 

 veined (Fig. 526). 



Venation or Nervature: Fig. 524, Pinnately veined leaf of Castanea: a, midrib; b, secondaries: o, 

 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. 

 629. Costinerved leaf. 



In the second form there is but one, or a comparatively few original 

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

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

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

 not anastomose or intercommunicate at their distal ends. When they 



