Polypodium. 
i 67 
two-thirds of fibry peat to one of leaf-mould, mixed with sand and rubble. Water must not 
be allowed to settle about the roots, free drainage being essential. 
THE LIMESTONE POLYPODY: POLYPODIUM ROBERTIANUM, Hoffm. 
This species, which is also known as P. calcareum , Smith., is by some writers considered 
as a variety of the preceding — an opinion in which, after the examination of a large series 
FROND OF POLYPODIUM ROBERTIANUM. 
of specimens, we do not feel inclined to concur, it is a plant of rigid, upright habit, and is 
altogether a more stiff-growing, upright species than P. Dryopteris ; the shape of the fronds, 
as is shown by the figures, differs a good deal from that of the fronds of P. Dryopteris. The 
last-named plant, too, although soft to the touch, is perfectly smooth ; P. Robertianum, on the 
contrary, is covered throughout with a glandular pubescence, which is especially noticeable upon 
the rachis and stipes. 
The distribution of the Limestone Polypody in England affords some very curious 
problems. It is now some twelve or fourteen years since we were shown two specimens which 
had been gathered in a wood near High Wycombe, in Buckinghamshire ; the bona fides of 
the collector was above suspicion, but the most careful searching in the wood failed to 
detect other specimens ; and this appears to be the only occasion upon which it has been found 
in that county. In Oxfordshire it was, we believe, once found in Wychwood Forest, but this 
was many years ago. The other English counties recorded for it are Somerset, Wiltshire, 
Gloucester, Hereford, Stafford, Worcester, Shropshire, Derbyshire, Yorkshire, Lancashire, Durham, 
