202 HISTORY OP BRITISH FERNS. 



ness, and then by a moderate fresh supply to produce a 

 continued change of the watery element. For the same 

 reason, and to prevent the souring of the soil, which always 

 takes place more or less when it is in contact with stagnant 

 water, an outlet at the bottom of the case should be care- 

 fully provided, by which all the free water at least, which 

 drains through after the soil has been irrigated, may be 

 removed as it accumulates. 



As to aspect, the northern is decidedly the best, princi- 

 pally for the reason, that in such a situation the sun has 

 less influence on the temperature of the interior of the 

 case ; and extremes of confined heat would be anything but 

 favourable to these plants. 



The appearance of the case would, no doubt, be improved 

 by covering the soil entirely with living green Sphagnum 

 moss, which, if neatly packed on the surface with the tops 

 of its stems uppermost, would continue to grow and retain 

 its verdure. Most of the species of Club-moss would prefer 

 to grow amongst the Sphagnum, which, as it made fresh 

 growth, should, to prevent its being drawn up and smother- 

 ing the plants, be neatly clipped down occasionally with a 

 pair of scissors. 



The interest of such a collection, so far as their appear- 



