be permitted to occupy something more than our usual space in 
endeavouring to explain in what way we conceive it possible to name 
the various forms of venation, so as to render them capable of being 
adapted to methodical description. 
This object will be most readily effected by describing the idea 
we attach to a simple leaf, of the most complete kind, in any common 
Dicotyledonous plant. 
Such a leaf has a main bundle of vessels running through its axis 
from the base to the apex, which bundle of vessels is called a costa. 
It is usual to ascribe only one costa to a simple leaf, all lateral 
ramifications, from whencesoever they proceed, being considered to 
be lateral veins. It is, however, more natural to understand that in 
truly lobed leaves, which may be supposed to be simple leaves 
approaching a state of composition, there are several costae, the 
bundles of vessels commonly called lateral veins, and passing from 
the base of the leaf to the apex of each lobe in an uninterrupted right 
line, being in fact of that nature; as is plainly shewn by the dis¬ 
position of the veins which pass from each costa. 
The costa sends forth, alternately right and left along its whole 
length, ramifications (vena primaria) of less dimensions than itself, 
but more nearly approaching it than any other veins. These venae 
primariae proceed from the costa at various angles, and are carried 
towards the margin ; when they arrive at a certain distance from the 
axis they take a curve in the direction of the margin, again bend 
inwards towards the axis, and in this course form an anastomosis with 
the back of the vena primaria which lies next them. That part of 
the vena primaria which is beyond the anastomosis thus described, 
having a curved direction, may be called the vena arcuata. Between 
the latter and the margin, other veins, with a similar direction and of 
similar power, occasionally intervene; as it will sometimes be neces¬ 
sary to speak of them, they may be distinguished by the name of 
vena externa. The margin itself and these last are connected by a 
fine network of minute veins, which we would designate as venula 
marginales. 
From the costa are often produced, frequently at right angles with 
it, and alternate with the venae primariae, smaller veins, which may 
be considered incomplete venae primariae, and may be not improperly 
named vena costales. The venae primariae are themselves connected 
by veins which proceed from each, and anastomose in the area 
between them. These veins, where they immediately leave the vena 
primaria, we would name venula propria, and the reticulation formed 
by the anastomoses of their extremities, venula communes. 
We have said that the venae primariae proceed from the costa at 
angles of various degrees ; we conceive that terms should be employed 
to explain nearly at what angle they leave the costa; as, subparallela 
when they form an angle of 10° to 20°, as in most monocotyledones; 
patentes, if the angle varies from 40° to 60°, as in the plant which has 
