8 
INTRODUCTION. 
there can be no doubt about their existence in every county of Britain ; although 
published records will not enable any one to make the assertion on evidence. 
Others, on the contrary, are much more limited in their range, being absent from 
the southern, or northern, or lowland counties of England. Only a few species 
can be called decidedly rare. The mountain valleys below 1500 or 2000 feet are 
the head quarters of Polypodiaceae ; very few species wholly shunning the moun- 
tain tracts, and a still less number being exclusively confined to the higher 
parts of the hills. The specimens are numerous amongst the mountain valleys, 
in the western counties, and in the vicinity of the coast. On the contrary, they 
are few in marshes, on low 7 plains, dry moors, exposed downs, and places destitute 
of woods or other shelter from sun and wind. Apparent exceptions to the 
favorable or unfavorable effects of any of these conditions, may usually be ex- 
plained by excess in some other and counteracting one. Thus, the salt spray and 
violent winds of the western shores are highly unfavorable to the growth of 
most Ferns, though otherwise their humidity of atmosphere would be favorable ; 
and accordingly whilst the exposed shores and cliffs may be almost without Ferns, 
caves and sheltered ravines in their immediate vicinity may be numerously 
tenanted. For the most part, however, even situations that are unsuitable to the 
majority of Ferns, have their own appropriate species. Thus, Asplenium mari- 
num flourishes on cliffs exposed to the sea ; Pteris aquilina and Bleclinum often 
grow on the unsheltered heaths, in places open to sun and wind ; Asplenium ruta- 
muraria and As. Adiantum nigrum live in the crevices of dry walls and rocks. 
There are, however, no aquatic Ferns, and scarcely any of the Polypodiaceae, that 
can be designated marsh plants ; unless that occupant of swampy bogs, Aspidium 
tlielypteris, be called a tenant of the marshes. A light friable soil, and more 
especially that formed by the decay of tree leaves, mosses, or other vegetables, 
is suitable to the roots of most Ferns ; but some delight in limestone soils, as 
Grammitis ceterach, Polypodium calcareum, and Cistopteris fragilis ; whilst the 
Asplenium septentrionale and Woodsia ilvensis seem to affect the basaltic trap and 
the harder primary rocks. The operations of human industry have greatly 
interfered with the natural distribution of Ferns in this country. They have been 
banished from our roads, corn fields, meadows, and artificial pastures ; and the 
cutting of peat, and burning of heath and furze, often check the growth of species 
fitted to thrive in places where these operations are performed. On the other 
hand, our hedge-banks, loose stone fences, old buildings, and neglected quarries, 
frequently become artificial fernetums, by affording suitable habitats for several 
species. These remarks on the distribution of Polypodiacese will be understood 
to apply to the island of Great Britain only. Ireland has tw 7 enty-six species of 
dorsiferous Ferns ; but of their range and distribution within that island little is 
known. All those of Ireland are natives also of England.* 
• Avery interesting and extended paper upon the distribution of ourFcrns.by Mr. Watson, will 
be found in “ The Transactions of the Edinburgh Botanical Society,” Part II. The above remarks, 
together with others of a corresponding character, inserted at other places, were kindly con- 
tributed to the Author, in writing, some lime since. They may not agree, therefore, in precise 
words with the Edinburgh paper. 
