GENERA OF FERNS AND THEIR CLASSIFICATION. 63 
natural groups and sequences are obtained than by a, 
strict adherence to the artificial characters afforded 
by the fructification and venation. Among Ferns 
no single organ alone affords characters sufficient for 
general systematic purposes. Were the principle 
upon which Linnaeus acted — that is, a strict adherence 
to the fructification alone — applied in its integrity 
to the enormous mass of Ferns now known, — and it 
would be quite possible to do so, the most incongruous 
plants would be associated under one genus, and the 
magnitude of the genera would be quite overwhelming. 
The same would be the case were venation alone or 
habit alone to be taken into consideration. In some 
instances, however, a marked difference in one set of 
characters indicates well-defined groups ; but as a 
general rule a combination of differences in two or 
more sets is requisite. Great difference of opinion 
exists as to what is and what is not a genus ; but so 
long as plants are distributed into well-circumscribed 
groups of not too great an extent, it appears to me 
that it is a matter of little importance whether those 
groups be termed genera, sub-genera, or sections. 
For my own part I prefer regarding them as genera. 
It has not been without due consideration that I have 
arrived at this conclusion. It also saves a great deal 
of unnecessary trouble, both in speaking and writing 
about Ferns, it being more easy to say and write 
Elaphoglossum conforms , than Acrostichum ( Elapho - 
glossum ) conforme, or Gymnogramme tomentosa, than 
Gymnogramme ( Eugymnogramme ) tomentosa, &c. Also 
by studying the character of the smaller groups indi- 
vidually, and treating them as genera, their nature is 
at once brought to the mind, without having to think 
