92 MORPHOLOGY OF LEAVES. 



Basal-nerved, that is, with the nerves all springing from the 

 base of the leaf, and 



Costal-nerved, springing from a midrib or costa. Either may be 



Rectinerved, the nerves running straight from origin to apex 

 or margin of the leaf, as the case may be ; 



Curvinerved, when curving in their course, as in the leaves 

 of Funkia and in Canna ; 



Flabellinerved, where straight nerves and ribs radiate from the 

 apex of the petiole, as in Fan-palms and the Gingko tree. 



174. In typical parallel- veined leaves, all reticulation is con- 

 fined to minute and straight cross- veinlets : in many, these are 

 coarser, branching, and reticulated ; in some, as in Smilax and 

 Dioscorea, only the primary ribs or strongest nerves are on the 

 parallel- veined plan ; the space between being filled with reticu- 

 lations of various strength ; thus passing by gradations into 



175. Reticulated or Netted- veined leaves. In most of these, 

 from one to several primary portions of the framework are 

 particularly robust, and give origin to much more slender ram- 

 ifications, these to other still smaller ones, and so on. The 

 strong primary portions are RIBS (costa) ; the leading ramifi- 

 cations, VEINS (venae) ; the smaller and the ultimate subdivisions, 

 VEINLETS (venulce) . All or some of the veins and veinlets are 

 said to anastomose, i. e. variously to connect with those from 

 other trunks or ribs, apparently in the manner of the veins and 

 arteries of animals, forming meshes. But, as there is no opening 

 of calibre of one into another, the word is etymologically rather 

 misleading. More properly, it is said that the veins or veinlets 

 form reticulations or net- work. A primary division of reticulated 

 leaves, and indeed of nerved leaves also, into two classes, is 

 founded upon the number of primary ribs. 



176. There may be only a single primary rib ; this traversing 

 the blade from base to tip through its centre or axis (as in Fig. 

 142, 152-156) is called the MIDRIB. There may be others, gen- 

 erally few (one, two, three, or rarely four) , rising from the apex 

 of the petiole on each side of the midrib, running somewhat par- 

 allel with it or more or less diverging from it : these are lateral 

 ribs. Among parallel- veined leaves, the Banana, Canna, &c., 

 have a single rib, from which the veins (in the older nomencla- 

 ture here called nerves) all proceed. Most Lilies and the like 

 have several approximately parallel ribs, but the midrib pre- 

 dominant: in other cases, the midrib is no stronger than the 

 others. In Fan-palms, the ribs are radiately divergent, giving 

 a fan-shaped or rounded outline to the blade. In reticulated 

 leaves, in which the veins all spring from the ribs, tht two 



