130 
ORGANOGRAPHY. 
BOOK I. 
to the belief that the structure and function of those two parts 
are as widely different as the structure and function of a vein 
and a nerve in the animal economy ; else why should such 
caution be taken to distinguish them ? But, in fact, there is 
no difference whatever, except in size, between the veins and 
nerves of a leaf. 
For the sake of obtaining great precision in describing such 
a very important and various-formed organ as the leaf, many 
terms have been invented, especially by Link and De Candolle, 
which, although not used in daily parlance, are important where 
brevity and precision are required. Without exactly adopting 
the nomenclature of either of these distinguished writers, it 
appears that upon it a system of names may be founded, to 
which the systematist can have little to object. 
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 should be extended to all main 
veins proceeding 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 parti- 
cular set of veins. 
56 
The midrib (Jig, 56. 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 may be called primary veins (Jig. 56. 3). They 
diverge from the midrib at various angles, and pass to the 
