INTRODUCTION. 37 
peculiarities, features of generic importance. Others, as Bory, 
Gaudichaud, Kaulfuss, Blume, &c., made use to some extent of 
characters derived from the venation; but subsequently characters 
derived from this source have been extensively employed, especially 
by Presl, J. Smith, and Fée, and arrangements founded thereupon 
are generally adopted at the present day. Indeed, this feature is 
made the basis of most modern methods of classifying Ferns. — — 
We have elsewhere* quoted the remark of the late Robert Brown, 
to the effect that for the purpose of subdivision, “the most obvious 
as well as the most advantageous source of character, seems to be 
the modifications of the vascular structure, or the various ramifica- 
tions of the bundles of vessels or veins of the frond, combined with. 
the relation of the sori to their trunks or branches.” + That learned 
and lamented botanist seems indeed to have had chiefly in view the 
formation of sub-genera, but the whole of the series of groups known 
as genera, sub-genera, and even species, are so highly artificial and 
arbitrary, that the exact use to be made of these characters becomes 
amere question of words and of convenience. At least in cases 
where the groups are so large and varied as to require the adoption 
of many sub-genera, as in the ancient Polypodium for example, it 
becomes less complex to consider the lesser divisions as genera, 
rather than as sub-genera, and the one course is as. correct, 
technically viewed, as the other. To us, therefore, it seems most 
convenient to adopt, but not to excess, the general principle of 
employing the venation as a supplementary generic character. 
Then, as to its value. Looking at the question of venation as 
illustrated by the great and universally adopted natural divisions of 
flowering plants, its use as a source of generic character in the 
case of the Ferns rests upon better ground than that of mere con- 
venience. The constant and unvarying occurrence of parallel free 
* Moore, in Proceedings of the Linnean Society, ii. 210. 
+ R. Brown, in Horsfield's Plante Javanice, 3. 

