XIV INTRODUCTION. 



the latter are particularly useful, they speedily cover 

 the earth and stones, and keep the surface in that state 

 of moisture which is so very advantageous. All kinds 

 of grasses, on the contrary, should be exterminated, 

 for they are of so rapid a growth, and vigorous a 

 nature, that they quickly overpower, weaken, and 

 finally destroy the more delicate among the Ferns. 



There is one species, Trichomanes speciosum, which 

 in a state of nature has its fronds always wet; it 

 invariably grows within the spray of waterfalls, or in 

 similar situations, where it is constantly supplied with 

 the needful moisture. This I find a most difficult 

 situation to imitate, but it may be managed by sus- 

 pending above the Fern a vessel containing water, 

 which shall be allowed to drop slowly on a stone, or 

 other hard substance in the neighbourhood of the 

 plant, the fronds of which will be wetted by the 

 sprinkling caused by each drop. Polypodium 

 Phegopteris and Cystopteris fragilis benefit greatly 

 by a similar treatment. 



There is one Fern, Asplenium marinum, which 

 hitherto I have failed to cultivate in anything like its 

 natural luxuriance ; this species grows on the most 

 exposed rocks on our bleakest shores, and yet I 

 believe it has never been cultivated in the open air 

 with success : in a temperature of 70 Fah. it will 

 grow with vast rapidity ; and with a lower temperature, 

 with artificial protection, it also answers very well. 



Adopting this plan of cultivation, I have possessed the 

 opportunity of observing the changes that took place, 



