CULTIVATION. 351 



number of species of exotic Perns sufficiently hardy 

 to bear the cold of our winters is very limited^ much 

 less than is generally believed^ the chief of them 

 being natives of North America, which, with the 

 British species, amount to about 80 in all } therefore 

 the extent of space required for a simple collection of 

 hardy Perns is small ; an area of 60 feet by 10 will be 

 ample, and which may be either on the side of a slope, 

 or between two slopes with a path in the centre and 

 open at one end only ; or it may be a raised oblong 

 mound with a path all around it. If not confined to 

 a strictly scientific collection, and space to be had, an 

 interesting natural glen may be formed by introducing 

 other plants conspicuous for their large foHage. 



It has been already stated, that although our small- 

 growing native and several exotic species, such as the 

 rock Asplenioe, Woodsia, &c., endure the extremes of 

 heat and cold in their native localities, they neverthe- 

 less suffer by full exposure under artificial cultivation ; 

 it is therefore necessary to plant them on the rockery, 

 so that they can readily be protected in winter; an 

 inverted flower-pot, placed over each plant and covered 

 with leaves, or some loose material analogous to the 

 covering of snow of their native country, is a good 

 protection against being injured by excess of moisture 

 or severe cold. Where the rockery is to be carried 

 out on a large scale, then oaves and chasms may readily 

 be constructed, and with a natural or artificial head of 

 water they can be kept moist by the constant drop- 

 ping and spreading spray; thus making appropriate 

 positions for the natural growth of Adiantwn Cappilus, 

 Hymenophyllem, &c. But when a full collection of the 

 many varieties of Bculopendrium, As^plenium, Lomaria, 



