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 small pipe, which can be 



