CULTIVATION. 379 



rocks. As regards the design of any structure in- 

 tended to be wholly or partially devoted to the culti- 

 vation of Ferns, it is of course a good deal a matter 

 of taste and convenience, as the system is available* 

 in almost any kind of structure, large or small, but 

 varying in the degree of economy in its construction. 

 To this end, the first consideration should be to 

 construct in a manner that will insure the necessary 

 amount of shade and moisture and (when required) 

 heat, with as little auxiliary assistance as possible. 

 Therefore if a lean-to house be adopted, the aspect 

 should be west or north-west, with the back consisting 

 entirely of wall. Should a span-roofed structure, how- 

 ever, be preferred, which indeed for all purposes is 

 much the best (and which will be here treated of as 

 a general example), its aspect should be north and 

 south, by which a shadier and consequently a moister 

 side of the house will be obtained, suitable for Ferns 

 of more or less delicate structure, such as the genera 

 Trichomanes and Hymenophyllum. A sunk house, in 

 the manner of a ditch or railway-cutting, is most 

 suitable, and will give ample height for the growth 

 of Tree Ferns, without the necessity of having high 

 side walls, and thus exposing a lessened portion of 

 the house's surface to the action of climatic vicissitude; 

 consequently a warm moist atmosphere may be main- 

 tained with but little assistance from artificial heat. 

 As a source of heat the hot-water apparatus is to be 

 preferred, on account of its economic utility, and 

 where practicable the pipes should be hidden as much 

 as possible with the rockery material. Perkins's sys- 

 tem of heating is perhaps the best for a house of this 

 kind; it consists of coils of sraall pipe, which can be 



