108 
ORGANOGRAPHY. 
BOOK I. 
anastomosis, or junction, with the back of the primary vein, 
which lies next them. That part of the primary vein which 
is between the junctions thus described, having a curved di- 
rection, may be called the curved vein. Between this latter 
and the margin, other veins, proceeding from the curved veins, 
with the same curved direction, and of the same magnitude, 
occasionally intervene : they may be distinguished by the name 
of external veins (fig. 53. 1). The margin itself and these 
last are connected by a fine net-work of minute veins, which 
I would distinguish by the name of marginal veinlets. From 
the midrib are generally produced, at right angles wdth it, and 
alternate with the primary veins, smaller veins; which may 
not improperly be named costal veins (fig. 53. 5). The pri- 
mary veins are themselves connected by fine veins, which 
anastomose in the area between them. These veins, when they 
immediately leave the primary veins, I call proper veinlets 
(fig. 53. 4) ; and where they anastomose, common veinlets. 
The area of parenchyma, lying between two or more veins or 
veinlets, I name v/ith the old botanists intervenium. 
These distinctions may to some appear over-refined ; but I 
am convinced that no one can very precisely describe a leaf 
without the use either of them, or of equivalent terms yet to 
be invented. Upon these principles leaves may be con- 
veniently divided into the following kinds: — 
1. Veinless (avenium), when no veins at all are formed, 
except a slight approach to a midrib, as in Mosses, Fuci, &c. 
Leaves of this description exist only in the lowest tribes of 
foliaceous plants, and must not be confounded with the fleshy 
or thickened leaves common among the higher orders of 
vegetation, in which the veins are by no means absent, but 
only concealed within the substance of the parenchyma. ( See 
No. 10.) Of this De Candolle has two forms, — first, his 
fi?lia nullinervia, in which there is not even a trace of a 
midrib, as in Ulva; and second, his Jblia falsinervia^ in which 
a trace of a midrib is perceptible. These terms appear to me 
unnecessary; but, if they be employed, the termination nervia 
must be changed to venia. 
2. Equal-veined (cequalivenium), when the midrib is per- 
fectly formed, and the veins arc all of equal size, as in Ferns. 
