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 Hymcnophyllum. 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 atmosphei’e 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 
ns 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 
