Polypodiwm .] 
KERNS. 
25 
Svn. — Polypodium calcareum, Swz., Wilhl., Smith, Hook., Purt., Galp . — 
Polypodium dryopteris, Bolt., Dicks. — Polypodium dryopteris ft, 
With., 2nd. edit. Polypodium Robertianum, Hoffm. — Nephrodium 
dryopteris, Michx. 
Fig .—E.B., 1525 .—Bolt. 1 .— Ger. 1135. 
Des. — This is so similar to the last, that when dried they are 
scarcely to be distinguished, hence, the doubt of their claim as 
distinct species ; but when growing, the eye will instantly sec the 
difference between the two. The P. calcareum is known from its 
root being thicker and less creeping, its frond rather larger in size, 
much more rigid, quite upright, and of a dark green color ; its lobes 
more deeply cut, and stem more scaly towards the base, and on the 
upper part sprinkled over with fine white minute hairs ; its sori are 
browner and more numerous. The minute pubescence seen on this 
species is most observable on luxuriant and fresh plants. It is, I 
believe, a constant and decided character, in which opinion I am 
supported by Mr. Wilson and Mr. Babington, than whom few are 
better able to form a correct judgment. The latter gentleman ob- 
serves, that the microscope shows every particle of this pubescence 
or mealiness to be a minute, stalked gland. 
Mr. Newman, in his beautifully-illustrated book on Ferns, blends this with 
the former species ; yet his figures show strongly-marked differences. Both of 
us no doubt argue according to our respective means of observation ; and after 
a very careful re-examination of both the species in my own and Sir J. Smith’s 
herbarium, and also as growing in Kew Gardens, I see no reason to alter a single 
word in the above descriptive characters. Whether the size of the two be of 
moment is the only thing which appears of little certainty ; but the rigid erect 
habit, and dark color are very characteristic, even without noticing the pubescence. 
Indeed, whatever doubt I may have of the distinctness of certain others of the 
Ferns, I cannot for an instant consider the present and former species identical ; 
let it be observed, however, that in the case of these, as well as some other species, 
the same herbarium often contains but the commoner plant, which is the P. 
dryopteris, yet some of the specimens may be under the name of P. calcareum, 
and too often does it happen, that the receiver of a specimen, taking for granted 
that such is correctly named, makes it a guide for his own future judgment, and 
thus an error becomes perpetuated. 
Hab. — Arncliff and Gordale, Yorks., Mr. R. B. Bowman. Near Lancaster, 
Mr. Gibson. Sheddin Clough, three miles from Burnley, Lane., Mr. Ley land. 
Common about Settle, Yorks., Mr. J. Taiham. Matlock Bath, Derbys., Dr. 
Howitt. Road-side under the Lover’s Leap, near Buxton, Derbys., Mr. H. C. 
Watson. Cheddar Cliffs, Somers., Mr. W. Christy. Box Quarries, near Bath. 
Mr. Flower. Not found in either Scotland or Ireland. 
/,^n» /fcewt. C/t , .X r — 
Geo. — Recorded by Pursh and Michaux as occurring throughout North 
America from Canada to Pennsylvania, and no doubt this is correct, as the 
description of Pursh so exactly accords with our plant ; though Swartz says that 
it is found in England only. 
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