INTRODUCTION. 
9 
to union or division of reputed species, but 35 is the number most generally- 
received. These bear a proportion to flowering plants (reckoning the latter 
at 1400) of 1 to 40. The order has a great numerical predominance over 
the other orders of Filicales, &c., all taken together ; the proportion of its species 
being to those of the other three orders, as 6 to 1. And since the most 
abundant and widely-ranging species of Ferns are also to he found amongst the 
Polypodiacese, the effect of this order in the general vegetation of our island 
much exceeds that of the allied orders of Ferns. Of the six species referred to 
other orders, one is exclusively an inhabitant of Yorkshire (if it really be there 
still) ; namely, Trichomanes brevisetum ; a second, Ilymenophyllum Tunbrigense, 
is local ; a third, H. Wilsoni, though much more plentiful, is limited to the 
northern and western counties; whilst the other three, theOsmunda, Botrychium, 
and Ophioglossum, though widely scattered through Britain, are by no means so 
generally present as many of the Polypodiacese. Several of the British dorsiferous 
Ferns are so widely and plentifully scattered throughout the island, that there 
can he 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 mountains valleys below 1500 or 2000 feet are 
the head quarters of Polypodiacese ; 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 countries, and in the vicinity of the coast. On the contrary, they are 
few in marshes, on low 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 marinum 
flourishes on cliffs exposed to the sea ; Pteris aquilina and Blechnum often 
grow on the unsheltered heaths, in places open to sun and wind ; Asplenium 
rutamuraria 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 
thelypteris, 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 limestones soils as 
Grammitis ceterach, Polypodium calcareum, and Cystopteris fragilis ; whilst the 
Asplenium septentrionale and Woodsia ilvensis seem to affect the basaltic trap 
