184 THE LEAF 



acuminate, require no definitions in addition to those which have been 

 apphed to simihir forms of the apex. 



When the two sides of the base are straight, and come to an acute 

 point, it is called Cuneate or Wedge-shaped (Fig. 518). 



A base the form of which yields later to a sudden downward ])rolonga- 

 tion or acumination is called Produced (Figs. 516 and 519). 



In all forms of the cordate base the greatest care must be taken to 

 specify the precise character both of the sinus and of the lobes. The 

 former must have its form or outline specified, as well as the angle 

 which it makes. It should, moreover, be carefully noted whether the 

 leaf-base at the summit of the petiole be produced into the sinus, in 

 which case it is called Intruded (Fig. 519). Sometimes the lobes of a 

 cordate base will meet one another, or even overlap. 



The forms of the lobes are also capable of taking descriptive titles 

 similar to those characterizing the lamina in general. The principal 

 of such terms are Auriculate, when the lobes are rounded similarly 

 to the lobe of the human ear (Fig. 521) ; Sagittate, when pointing down- 

 ward, and acute, like the lobes of an arrow head (Fig. 520) ; Hastate or 

 Halberd-shaped, when turned outward (Fig. 522). 



A base is Oblique or Inequilateral when descending lower upon one 

 side than upon the other (Figs. 521 and 523). 



Venation or Nervature. — Bundles which obviously separate from one 

 another at or near or below the base of the blade, and maintain their 

 course well toward the apex or margin, are called Costae or Ribs if 

 equally prominent (Fig. 527), nerves if lateral and markedly less promi- 

 nent than one or more of the central ones (Fig. 529). 



The central one, whether there be others or not, is the Primary or 

 Midrib (Fig. 524, a). Branches or ribs or nerves are called A'eins, and 

 they are distinguished as Secondaries (6) when departing from the mid- 

 rib, Tertiaries (c) when departing from Secondaries, and so on. In 

 palmately veined leaves, the central is called the IMiddle Primary, the 

 other, the Lateral Primaries. The middle one is here also called the 

 midrib, if distinctly stronger than the others. Secondaries of lateral 

 ribs or nerves must be especially so designated in description. Very 

 small veins are called Veinlets. 



The greatest importance in descriptive terminology pertains to the 

 classification of leaf-\'enation, owing to the frequency with which leaves 

 must be identified in such a fragmentary state that there is little beyond 

 the surface and venation, with possibly a portion of the margin, to 

 assist us. 



