248 THE FLORIST. 



which latter situation their absence is to be attributed rather to the 

 bleak exposure than to the absolute heig-ht. The number of our 

 dorsiferous Ferns will be estimated variously, according to the views 

 entertained with respect 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, all taken together ; the proportion of its species being to 

 those of the other three orders, as 6 to I. And since the most 

 abundant and widely- ranging species of Ferns are also to be 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 exclu- 

 sively an inhabitant of Yorkshire (if it really be there still) ; namely, 

 Trijhomanes brevisetum ; a second, Hymenophyllum tunbridgense, 

 is local ; a third, H. Wilsoni, though much more plentiful, is limited 

 to the northern and western counties ; whilst the other three, the 

 Osmunda, 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 be no doubt about their existence in every county of Britain ; 

 although published records will not enable any one to make the as- 

 sertion on evidence. Others, on the contrary, are much more limited 

 in their range, being absent from the southern, or northern, or low- 

 land counties of England. Only a few species can be called decid- 

 edly rare. The m.ountain valleys below 1500 or 2000 feet are the 

 head quarters of Polypodiaceae ; very few species wholly shunning 

 the mountain tracts, and a still less number being exclusively con- 

 fined 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 plains, dry moors, exposed downs, and places destitute of woods 

 or other shelter from sun and wind. Apparent exceptions to the 

 favourable or unfavourable effects of any of these conditions may 

 usually be explained by excess in some other and counteracting one. 

 Thus the salt spray and violent winds of the western shores are 

 highly unfavourable to the growth of most Ferns, though otherwise 

 their humidity of atmosphere would be favourable ; and accordingly 

 whilst the exposed shores and cliffs may be almost without Ferns, 

 caves and sheltered raj^ines in their immediate vicinity may be nume- 

 rously 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 clifts exposed to 

 the sea ; Pteris aquilina and Blechnum often grow on the unshel- 

 tered heaths, in places open to sun and wind ; Asplenium Ruta mu- 

 raria and A. Adiantum-nigrum live in the crevices of dry walls and 

 rocks. There are, however, no aquatic Ferns, and scarcely any of the 

 Polypodiacese that can be designated marsh plants ; unless that occu- 

 pant of swampy bogs, Aspidium Thelypteris, be called a tenant of the 



