56 THE FLOWERING PLANT. 



i.e., the manner in which the vascular bundles, popularly known 

 as veins, nerves, or ribs, are distributed. These are generally 

 visible externally, especially on the under side, where they may 

 project considerably. It may happen, particularly in fleshy 

 leaves, like those of the stonecrop, that this is not the case. 

 Dissection shows, however, that they are present, though not 

 obvious externally, so that the term hidden-veined may con- 

 veniently be applied. Two principal kinds of venation are dis- 

 tinguished, parallel and reticulated. In the former, which is 

 characteristic of monocotyledons, the chief veins, without under- 

 going division, run more or less parallel with one another, either 

 from base to apex, or from a central midrib to the margin. 

 Their course is either straight or curved. Most of our common 

 monocotyledons are basal-veined, i.e., possess no midrib, as may 

 be seen, for instance, in grass leaves (fig. 10), iris, lily of the 

 valley, Sec. Many exotics, such as the banana, illustrate the 

 costal-veined arrangement, in which a midrib is present. There 

 is, however, no sharp line of demarcation between these two 

 methods of distribution. If in a costal-veined leaf we suppose 

 the midrib to be telescoped, then the lateral veins would radiate 

 from the base of the leaf in a fan-like manner, their parallelism 

 being lost. The leaves of fan-palms are veined in this way. 

 Parallel-veined leaves, as a rule, do not exhibit anything like a 

 network in the arrangement of their vascular bundles, but very 

 small veins or veinlets can often be seen running straight across 

 the interspaces between adjacent veins, and connecting these 

 together. In four British monocotyledons, of which the two 

 commonest are the black bryony and the wild arum, the vena- 

 tion resembles that of the second type, i.e., the reticulated 

 or netted, which is characteristic of dicotyledons. The lamina 

 is here traversed by a complicated and irregular network of 

 small veins (fig. 13). The leaves of dock and apple furnish 

 good examples, respectively coarse and fine. This sort of vena- 

 tion presents two chief varieties. Compare the leaves of beech, 

 Spanish chestnut, or lilac with those of ivy, sycamore, or garden 

 geranium. On the one hand, the lamina will be seen to be 

 traversed by a central midrib, giving off branches in a feather- 

 like manner (fig. 13); on the other, several strong veins will 

 be noticed, radiating from the attachment of the petiole. In 

 both cases a great deal of branching may be observed, the 

 ultimate branchlets uniting or anastomosing into a network. 

 The leaves described, and others like them, are pinnately or feather- 

 veined and palmately or radiately -veined. The relation between 

 these two kinds of veining is similar to that existing between the 

 costal and radiate types in monocotyledons, and numerous grada- 



