FORMATION OF ROCK-WORK. 171 



ature and dry atmosphere. The only practicable way of 

 arresting them is by syringing or immersing as for Green 

 Fly. For further information on this point see chapter on 

 insects. 



There are no special soils necessary for the amateur to 

 trouble himself about in cultivating his parlor flowers. For 

 our opinions at length on this head, see chapter on soils. 

 Neither should he tamper with guano or other fertilizers ; 

 equalization of temperature and moisture will secure the 

 end desired. If he wishes to increase his plants, full di- 

 rections will be found under the head " Propagation." 



CHAPTER XXV.. 



FORMATION OF ROCK-WORK. 



This feature of pleasure ground decoration is generally 

 necessitated by circumstances; if the ground which has to 

 be chosen for that purpose is naturally stony, it often be- 

 comes the cheapest way to get rid of the stones, grouping 

 them so that they become ornamental. They may often 

 thus be used to advantage in forming breaks or screens, to 

 hide the flower garden from the vegetable or fruit garden ; 

 in this way they are laid up in rugged walls, the inter- 

 stices filled with soil and covered with hardy perennial 

 plants. Locations where rocks exist in their natural con- 

 dition can often be made highly interesting and ornament- 

 al by setting out plants of a drooping or trailing habit 

 to overhang among them. Among those suitable for such 

 purpose are : 



Achilleas, of creeping growth, Linnsea borealis, 



Campanulas, of creeping growth, Lychnis grandiflora, 



' Crucianella stylosa, Lyaimaehia nummularia, 



. Cerastium tomeutosum, Orobus veraus, 



