62 



DESCRIPTIVE BOTANY. 



PART I. 



leaf is termed its "venation" or "nervation" the 

 course of the vessels bearing some resemblance to the 

 distribution of veins and nerves in certain parts of the 

 animal structure. The bundles of vessels which com- 

 pose the veins, maintain a nearly parallel course in 



their passage through the petiole, and are closely con- 

 densed together ; but on arriving at the limb, they 

 separate, and are distributed in various ways ; all of 

 which may, however, be referred to one or other of 

 two classes, called the " angulinerved," and the " curvi- 

 nerved," disposition. The former of these is eminently, 

 though not exclusively, characteristic of dicotyledonous 

 plants ; and the latter equally predominant among such 

 as are monocotyledonous. 



(72.) Angulinerved Leaves. In these, the vessels, 

 after entering the limb, either branch off immediately 

 from the apex of the petiole, arid form several strong 

 veins ; or they form one midrib, from which secondary 

 veins are given off on either side, and which at their 

 origin, maintain a straight course for a short distance. 



