CHAP. II. 
LEAVES. 
107 
the veins of leaves are at present described ; whence it hap- 
pens that no precise idea can be attached to the different terms 
that have been contrived to designate particular forms of 
venation. 
A third objection is this, — that, while slight modifications 
in the arrangement of the veins have received distinctive 
names, others of much greater importance, and of a more de- 
cided character, have received no distinctive appellation what- 
ever. For these reasons, the practical weight of which I have 
long experienced, it has occurred to me that the following 
changes in the language used in speaking of venation will be 
found better, at least, than that for which they are substituted, 
if they are not entirely what could be desired. 
It has been usual to call that bundle of vessels only which 
passes directly from the base to the apex of a leaf the rih or costa, 
or midrib. This term I would extend to all main veins which 
proceed directly from the base to the apex, or to the points of 
the lobes. There is no difference in size in these ribs; and 
in lobed leaves, which may be understood as simple leaves, 
approaching composition, each rib has its own particular set 
of veins. 
7 
The midrib {Jig, 53. 7) sends forth, alternately right and left 
along its whole length, ramifications of less dimensions than 
itself, but more nearly approaching it than any other veins : 
these I would call primary veins {fig, 53. 3). They diverge 
from the midrib at various angles, and pass to the margin of 
the leaf, curving towards the apex in their course, and finally, 
at some distance within the margin, forming what is called an 
