CHAP. II. 
LEAVES. 
129 
instances of the upper surface being hairy while the lower is 
smooth. 
The ramifications of the petiole among the cellular tissue of 
the leaf are called veins^ and the manner of their distribution 
is termed venation. This influences in a great degree the 
figure and general appearance of the foliage. The vein which 
forms a continuation of the petiole and the axis of the leaf is 
called the midrib or costa: from this all the rest diverge, 
either from its sides or base. If other veins similar to the 
midrib pass from the base to the apex of a leaf, such veins 
have been named nerves ; and a leaf with such an arrange- 
ment of its veins has been called a nerved leaf. In speaking 
of these parts, a leaf is said to be three^ or Jive^ or otherwise 
nerved, if the so-called nerves all proceed from the very 
base of the lamina, but it is called triple, quintuple, &c. nerved, 
if the nerves all proceed from above the base of the lamina. 
If the veins diverge from the midrib towards the margin, 
ramifying as they proceed, such a leaf has been called a 
venous or reticulated leaf. This is the sense in which these 
terms were used by Linnasus ; but Link and some others 
depart from so strict an application of them, calling all the 
veins of a plant nerves, whatever may be their origin or 
direction. 
The veins are, however, improperly called nerves, either in 
all cases, as by Link, or in certain cases only, when they have 
a particular size or direction, as by Linnaeus and his followers. 
Nothing is more destructive of accurate ideas in natural his- 
tory than giving names well understood in one kingdom of 
nature to organs in another kingdom of a different kind, unless 
it is the, perhaps, more reprehensible practice of giving two 
names conveying different ideas to the same organ in the 
same kingdom of nature. Thus, when the veins of a plant 
are termed nerves, it is naturally understood that they exer- 
cise functions of a similar nature to those of the nerves of 
animals: if otherwise, why are they so called? But they 
exercise no such functions, being mere channels for the 
transmission of fluid. Again, if one portion of the skeleton 
of a leaf is called a vein, and another portion a nerve, this 
apparently precise mode of speaking leads yet more strongly 
K 
