186 THE LEAF 



do, the term Reticulate is applied to them in a special or restricted 

 sense (Fig. 525). 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 secondary is arched upward into the secondary next 

 above (Fig. 525) . In such case it is important to note the comparative 

 distance from the margin at which the communication takes place and 

 the angle at which the two meet, as these characters are always constant 

 in the same species. In other cases the secondaries (or the ribs, as in 

 Fig. 568) are directly connected by straight and parallel secondaries 

 or tertiaries, or in still others (Fig. 516) by an irregular intervening 

 network of small veins. Secondaries connected by the first method 

 are usually also connected near the base with the midrib by a number 

 of curved tertiaries. 



When the principal veins or nerves of a leaf are straight, it is called 

 Rectinerved; when curved, Curvinerved. The latter term refers to a 

 regular and characteristic curve, not to a crooked course. Some leaves 

 are characterized by possessing waving or crooked nerves or veins. 



Two great classes of netted-veined leaves are recognized, the one in 

 which there is a main Rachis or midrib, from which secondaries 

 extend regularly toward the margin. This form is known as th e Penni-_ 

 nerved or Pinnately veined leaf (Fig. 524). The number of pairs of 

 secondaries, whether they originate exactly opposite to each other or 

 somewhat 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, their number and stoutness as compared with the midrib, 

 their comparative length and the position which they take in the leaf 

 are all important. The second great class of netted-veined leaves is 

 that in which a number of approximately equal ribs radiate from the 

 basal region. Such leaves are known as Palmatel;)^ or D i gitately 

 Veined (Figs. 527 and 528). There are, of course, many forms of inter- 

 grading (Figs. 529 and 568) 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 Basinerved (Fig. 528) ; 

 at others from the lower portion of the midrib, when it is called Costi= 

 nerved (Fig. 529). When the ribs or nerves are manifestly continued 

 downward into the petiole, the leaf is called Flabellatelv ^ nerved (Fig. 

 527). 



The Leaf-margin. — The manner in which the leaf-margin comes to 

 deviate from an entire condition has already been indicated. Three 



