38 THE BRITISH FERNS. 

| veins and of reticulated veins in the primary groups of flowering 
H plants, and the value assigned to them, are significant facis; and 
N importance may be equally claimed for similar differences among 
the Ferns. That some auxiliary character beyond that afforded by 
hi the sori and their covers, is required, is very commonly admitted ; 
for while the complete series of floral organs in flowering plants 
offer such numerous and varied characteristics for generic combi- 
nation, the differential characters to be drawn from the sori in 
| Ferns are exceedingly limited. And what auxiliary character is 
there so proper to be employed as the vascular structure of the 
|. plant with which the sori are so intimately connected? Expe- 
rience, moreover, attests that it may be relied on with perfect 
N confidence, for it is found, with a few insignificant exceptions, that 
| whatever condition of the venation occurs in a particular species, 
| that condition is constant to that species. 
|i The vascular system, as we have already stated,* must be regarded 

as of the highest importance in the economy of plants, even in 
reference to their propagation, for cases are not at all infrequent in 
which certain extraordinary means of development, namely, adven- 
titious buds, are formed in direct connection with it. In the Ferns 
particularly, those points of the veins which normally serve as 
the receptacles to which the spore-cases are attached, in other cases 
become viviparous, and develope gemme or buds instead of spores. 


| Though thus claiming systematic. importance for the venation in 
Ferns, and supporting its use as a source of generie character, we 
| are ready to admit that the question is not altogether free from 
i | anomalies, or without its difficulties ; these are, however, not greater 
| j than occur in the application of our imperfect knowledge to the 
classification of other groups of plants, where even with all the 
| variety of character afforded by the flower and seed, anomalous and 
dubious species are not uncommon; nor are the anomalies here 

i * Proceedings of Linnean Society, ii. 211; and Gardeners’ Chronicle, 1853, 86. 

