VENATION: MARGIN. 



87 



mer must have its form or outline specified 

 as well as the angle which it mates. 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. 434). 

 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 arc Auriculate 

 when the lobes are rounded similarly to 



the lobe of the human car (Fig. 435), Sagi- 

 tate when pointing downward and acute, 

 like the lobes of an arrow head (Fig. 436); 

 Hastate or Ilalberd-shaped when turned 

 outward (Fig, 437). A base is Oblique 

 or Inequilateral when descending lower 

 upon one side than upon the other (Figs. 

 435 and 438). 



The greatest importance in descriptive 

 terminology pertains to the classification 

 of leaf venation, 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 ns. The forms all fall within two 

 principal classes, which in general char- 

 acterize respectively the monocotyledons 

 and the dicotyledons. The former bears 

 its principal veins more or less parallel 

 with one another, and these are numerous. 

 Snch leaves are called Parallel Veined 

 (Fig, 439). In the second form there is 

 but one, or a comparatively few, original 



voins, 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. 387, &c.). These may or may 

 not anastomose or intercommunicate at 

 their distal ends. When they do, the term 

 Reticulate is applied to them in a special 

 or restricted sense (Figs. 388 and 421). In 

 leaves of the last-named class the details 



of the method of intercommunicating are 

 very important. Thus, in some cases, the 

 end of each primary is arched upward into 

 the next primary above (Fig. 388). In 

 guch case it is important to note the com- 

 parative distance from the margin at 

 which the communication takes place and 



the angle at which the two meet, as tliese 

 characters are always constant in the 

 same species. In other cases the primar- 

 ies (or the ribs, as in Fig. 474) are di- 

 rectly connected by straight and parallel 

 secondaries, or in still others (Fig. 421) by 

 an irregular intervening network of small 



reins. Frimaries connected by the first 

 method are usually also connected near 

 the base with the midrib by a number of 

 curved secondaries. "When the princi!»nl 

 veins or nerves of a leaf are straight they 

 are called Kectinerved, when curved, 

 Curvinerred. The latter term refers to a 

 regular and characteristic curve, not to a 

 crooked course. Some leaves are charno- 

 terized bj- possi^ssiiip: waving or crooked 



nerves or veins. Two great classes of 

 netted veined leaves are recognized, the 

 one in whic4i there is a main Rhachis or 

 midrib, from which primaries extend reg- 

 ularly toward the margin. This form is 

 known as the Fenni-nerved or Pinnately 

 veined leaf (Fig. 387). The number of 

 pairs of primaries, whether they originate 

 exactly opposite to each other or some- 

 what irregularly, is within fair limits 

 characteristic of the species and should be 

 stated. The same is true of the angle at 

 which they radiate from the midrib. In 

 the case of additional ribs or nerves of 

 such a leaf, the number and stoutness as 

 compared with the midrib, their compara- 

 tive length and the position which they 

 take in the leaf are all important The 

 second great class of netted-veined leav»*s 

 is that in which a number of approxi- 

 mately equal ribs radiate from the basal 

 region. Such leaves are known as Pal- 

 mately or Digitately Veined (Figs. 440 

 and 441). There are, of course, many 

 forms of intergrading (Figs. 442 and 474) 

 between such leaves and pinnately veined 

 leaves with secondary ribs or nerves. 

 Sometimes the nerves start from the very 

 base of the leaf, in which it is called Basi- 

 nerved (Fig. 440); at others from the lower 

 portion of the midrib, when it is called 

 Costi-nerved (Fig. 442). When the ribs or 

 nerves are manifestly continued down- 

 ward into the petiole, the leaf is called 

 Flabellately nerved (Fig- 441). 



The manner in which the leaf margin 

 comes to deviate from an entire condition 



