THEIR NOMENCLATURE. 455 
Hooker and Bentham still). Nevertheless, this was sound dis- 
crimination (borrowed from other observers) on the side of Dr. 
Arnott, for the two couples so formed bring each one of the four 
segregates into union with its next of kin; and we have only to 
split Arnott’s couples (or perhaps only one of the two couples) to 
work down to things pretty clearly distinct from each other by 
physiological characters. The dilatata and @mula seem to be 
sufficiently distinct, by several permanent characters; and if once 
clearly known, they cannot afterwards be confounded with each 
other. But the uliginosa of Newman, a variety diverging from 
cristata towards spinulosa, or vice versa, keeps these two latter in 
closer relationship ; seeing that botanists are ill agreed to which 
of the two it ought to be assigned. Sir William Hooker referred 
it to spinulosa. I thought him correct in this, while judging only 
from dried fronds. But after watching it in cultivation through 
some years, side by side with spinulosa, I now separate it from 
this latter and refer it to cristata. The three are closely alike in 
form and general habit, though divergent in the cutting of their 
fronds ; and when they are full-grown and perfect, they look wide 
apart from the living dilatata. I think that scarcely any botanist 
could confound this last with the others in a wood or swamp, 
although he might readily do so through book descriptions, or 
even in the herbarium. On young or weakly plants of dilatata 
and spinulosa the fronds are short and subtriangular. On older 
and vigorous plants they are deltoid-lanceolate in dilatata, deltoid- 
linear in spinulosa ; that is, lanceolate and linear, always tending 
to deltoid by the length of the lower wings, in much the same 
manner as angulare may be distinguished from truly lanceolate 
lobatum, or Filix femina from rheticum. 
Now going back some time in the chronological nomenclature of 
these ferns, we find Hudson’s Flora (1762, etc.) describing a 
Polypodium cristatum to represent them, with the addition of a 
Polypodium rhaeticum from Westmoreland, possibly to stand for 
a variety of one of them, not of Cystopteris fragilis. But we may 
hold it almost certain that Hudson had not seen either emula or 
true cristata; and if so, his Polypodium cristatum meant simply 
