DECEMBER. 
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or oftener divided on the same plan, and is then bipinnatifid, tripin- 
natijid, &c. Unless the lobes are very shallow indeed, this does not 
affect the application of the term costa, on which that of the entire series 
of names belonging to the veins is made to depend. Sometimes both 
modes of division occur together; for instance, a frond may be once or 
twice pinnate, with the pinnae or pinnules, as the case may be, pin- 
natifid. A frond which is once pinnate, and then has the pinna only 
pinnatifid, is properly designated pinnato-pinnatifid, and one which is 
twice pinnate and then pinnatifid is bipinnato-pinnatifid, and so on. 
The venation of the frond, which has been shown to mean 
the costa and its ramifications, presents great variety in different 
species, but it is, in a general way, quite constant in the same species. 
There are a few instances known, in which, for example, Ferns which 
usually have the veins free, have them here and there running together 
in particular fronds or parts of the fronds, but these are to be regarded 
as mere exceptions which prove the general rule, and are not often liable 
to be misunderstood. Indeed this inconstancy most generally happens 
in cases where some disturbance of the ordinary development has 
occurred. Thus in the Hart’s-tongue Fern, which normally has entire 
fronds and free veins, some of the monstrous varieties, in which the 
frond is narrowed and the margin broken up, have the veins altogether 
disarranged, so that they unite more or less frequently, but the cause 
is sufficiently evident; and so in other cases. 
It is the condition of the veins and the mode of their arrangement 
which has of late years been employed as an auxiliary character in 
distinguishing the genera of Ferns. This use of the venation, is, indeed, 
objected to by some botanists of high authority, who think that the 
fructification alone should furnish the generic character ; but however 
proper this view may be as regards flowering plants, where the organs 
forming the parts of fructification are numerous and varied, it does not 
appear to us equally so in the case of Ferns, where the so-called organs 
of fructification present few available differences, and where the species 
are nevertheless so numerous that some further distinguishing character 
is desirable in order to break up into groups of moderate size the large 
unwieldy genera of olden times. No auxiliary character has proved so 
useful, nor so constant, nor, we believe, so important, as the venation. 
This, indeed, is practically admitted, even by those who object to its use 
in distinguishing genera, for they willingly employ it as characteristic 
of sub-genera. Now the difference between a genus and a subgenus 
is so very trifling, depending entirely on the mere fancy of the indi¬ 
vidual botanist, that the admission of venation as a characteristic of 
subgenera may be taken as an admission of the whole question. Much 
of the importance we are inclined to claim for venation as a feature of 
generic value, rests upon the fact that it gives rise to the fructification. 
The spore-cases which form this fructification spring out of it; the 
receptacle to which they are attached is part of it; and this inti¬ 
mate connection with the fructification must give the venation in the 
Fern, a higher importance than could be properly attached to it in the 
case of flowering plants—among which, notwithstanding, the important 
differences of free and reticulated venation, run parallel with other 
features which mark the great primary groups of exogens and endogens, 
