56 THE FLOWERING PLANT. 
z.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 /idden-veined may con- 
veniently be applied. Two principal kinds of venation are dis- 
tinguished, parallel and reticulated. In the parallel variety, 
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, &c. 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, 7z.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- 
