hi) LindleT/s Theory of Horticulture. 429 



appearance, unaccountably killed, while another is left unhurt. 

 In order to protect plants from frost, we should study to have 

 the plants themselves, and the earth around, as dry as possible 

 towards the evening. The situation for plants liable to be hurt 

 by spring and autumn frosts should be as much elevated as 

 possible, in order to have the benefit of the wind in dispersing 

 the cold heavy air and bringing forward the warmer; in low situ- 

 ations, the cold air, being heavier, collects, and not being benefited 

 by the dispersion of the wind and bringing forward of warmer 

 air, plants are much more liable to be hurt by slight frosts in 

 such situations. Wherever possible, when the clearness and cold- 

 ness of the air indicate a tendency to frost, plants that are 

 worth the expense should be covered with the best nonconduct- 

 ing substance we can fall in with. Metals are the worst; if 

 polished and bright in the colour however they are better non- 

 conductors than when dark-coloured and rough ; wood is better ; 

 but, unless when saturated with moisture, woollen is the best 

 of any, from the confined air retained between the hairs of the 

 wool. Whatever covering is used, whether straw mats, bast 

 mats, cloth, or wood, they should be elevated above the surface 

 to be covered, so as to contain as much confined air as possible : 

 confined air is one of the worst conductors of heat ; the covering 

 will not radiate, or give out heat, till the confined air and cover- 

 ing are both heated above the state of the atmosphere; and the 

 transmission of heat will take place more slowly through the con- 

 fined air than any thing else : thus, for very little trouble, by elevat- 

 ing our coverings, we surround our plants or plant structures with 

 a substance which is very retentive of heat, and increases the 

 power of the covering in an immense degi*ee. The heat has most 

 tendency to ascend upwards, and this should be most guarded 

 against ; but it will also escape by the sides, and to confine the 

 air and heat completely, the plant or plant-structure must be 

 covered all round from the external air. Wall trees should 

 have a broad coping of wood on the wall, to prevent the ascent 

 of heat ; and woollen nets drawn before tender peaches, &c., 

 in cold nights, and carefullv removed in arood weather through 

 the day, are a great help, when not left on in all weathers. The 

 wall is best built of porous materials, as bricks, which retain the 

 heat from the confined air better than stone ; and they should be 

 built with hollow chambers, as advised by Mr. Loudon, for the 

 same purpose. Where painting is needed, white is the best colour. 

 To prevent the bad effects of cold east winds in the spring, caus- 

 ing the sap to descend in standard fruit trees, and destroying the 

 blossom when expanded, by the check it gives to the ascent of 

 the sap that should nourish it, the stems and branches should 

 be bound with straw ropes, and the ground mulched. Various 

 situations should be chosen, to protect tender shrubs and trees, 



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