CONSERVATIVE WALL AND BOEDER, ETC. 



735 



vious to wet, or has the property of throwing it 

 off ; the second by placing the protection so far 

 from the plant to be protected as to admit of a 

 body of air being confined between them, and 

 that in a quiescent state ; while the third can 

 only be effected by using some transparent or 

 semi-transparent material. Foi^ the former of 

 these the bast-mat is ill adapted ; its very con- 

 struction is the antipodes of the principle, and 

 reed mats are little better. Both are expensive 

 in the first instance, and are neither durable nor 

 conveniently put on and taken off. Netting and 

 straw in their various forms, as well as branches 

 of trees, fern fronds, &c., are only very super- 

 ficial protections, and greatly tend to shut out 

 the light from the plants ; they are useful, how- 

 ever, for protecting deciduous shrubs and trees 

 growing as standards, as netting can be thrown 

 over them, and secured to their stems in form 

 of a balloon ; and handfuls of straw, asparagus 

 haulm, fronds of fern, &c., can readily be tied 

 to the main branches, and so arranged that 

 the leading shoots may be partially covered. 

 Branches of trees, broom, &c., may be applied 

 in a similar manner, particularly the latter, as 

 it maintains its green colour, and is less offen- 

 sive to the sight. In this way we protect many 

 tender roses, and various deciduous trees and 

 shrubs, putting it on in November, and allowing 

 it to remain till March, when it is gradually re- 

 moved as the chances of severe frost disappear. 

 Bunting and canvass , either of which may be 

 dyed a green colour, may be advantageously 

 employed to envelop shrubs and trees, and, like 

 netting, if firmly secured round the stem to pre- 

 Tent the wind from entering, may remain on 

 during the whole vfinter. Both these last ma- 

 terials, from their flexibility, are well adapted 

 for mounting on rollers or otherwise, and being 

 let up and down in front of plants against a wall. 

 Protection is best secured when it is placed a 

 little distant from the plant, therefore shrubs 

 growing on lawns or in borders should have a 

 framework of wood placed around them, to 

 which the canvass should be secured, one of the 

 sides being so constructed that it may be occa- 

 sionally opened for the admission of air and 

 light — and this is the more necessary if the 

 canvass be thick and opaque. 



Cases of half inch boarding, covered at top with 

 a movable pavilion roof to throw off the rain and 

 snow, and having the side facing the south par- 

 tially filled with glass to admit light, and made 

 so as to open for the admission of air, are excel- 

 lent protectors ; but the best of all are glass 

 structures framed in pieces like ordinary hand- 

 glasses, and of sizes so as to cover the entire 

 plant, so that neither the leaves nor branches 

 come in contact with it. In severe frosts these 

 may be covered with canvass or similar material. 

 Whatever protection be used, it is important 

 that it should prevent the entrance of wet, for 

 the drier the plants are kept, the better they 

 will resist the cold. It is also essential that the 

 roots be prevented from becoming frozen or 

 saturated with moisture, therefore the surface 

 of the ground, as far as they extend, should be 

 covered with moss 3 or 4 inches thick, and 

 secured against displacement ; finely-sifted coal- 



ashes are also both an excellent non-conductor 

 of cold and corrector of damp. That portion of 

 the stem which connects it with the roots, known 

 as the collar of the plant, is the most suscept- 

 ible of the cold ; it is necessary, therefore, that 

 it be protected either by gathering up the coal- 

 ashes around it, or by enveloping it around with 

 a neat hay-band. 



More temporary yet effective protectors may 

 be found, particularly for small shrubs, by cover- 

 ing them with sea-kale pots, Ufting the lids off 

 occasionally, inverting large fiower-pots over 

 them ; and for plants of larger sizes, empty casks 

 or large boxes are good substitutes. 



In the application of covering it should be 

 borne in mind, that anything which obstructs 

 the free aspect of the sky arrests, in proportion, 

 the progress of radiation, and the slightest cover- 

 ing with cloth almost prevents it altogether. 

 Plants, therefore, to derive protection, should 

 have the covering material placed at a moderate 

 distance from them, so as to contain as much 

 confined air as possible. Air in a state of 

 quiescence is one of the worst conductors of heat 

 possible, and no covering will radiate or give 

 out heat till the covering, and the air confined 

 under it, are both above the heat of the atmos- 

 phere. Heat, having a natural tendency to escape 

 upwards, must be prevented from escaping in 

 that direction. It will also escape by the sides; 

 and therefore,' to confine it entirely, the plant 

 must be covered all round from the external 

 air. It would be difficult to procure, or even 

 apply, a perfectly air-tight covering, but such 

 openings as communicate directly with the ex- 

 ternal air may be guarded against, so as to pre- 

 vent the escape of heat. Thus, for example, the 

 ordinary covering of netting, be it ever so fine 

 in the mesh, affords comparatively little protec- 

 tion, because the heat escapes through the 

 meshes; and any number of courses of the same 

 would afford as little, if placed so that the 

 openings be exactly above each other; but by 

 alternately placing over each other the open and 

 closed parts, the escape of heated air, as well as 

 the entrance of cold air, is very much inter- 

 rupted. The heated air from within would have 

 to deviate as often from its direct line of escape, 

 as would also the cold air from without in 

 endeavouring to enter, as it meets with the 

 obstruction of the closed parts of the netting. 

 Mr Daniell, in Essay on Climate, has clearly ex- 

 plained this important point, and observes : 

 " Almost all the modes in practice of protecting 

 plants are founded on the doctrine of radiation; 

 and hence the fact should be kept constantly in 

 mind, that all bodies placed in a medium colder 

 than themselves, are continually giving out their 

 heat in straight lines, and that these straight 

 lines, when the body is surrounded by air, may 

 always be reflected back on the body from which 

 they emanate, by the slightest covering placed 

 at a short distance from them ; while, on the 

 other hand, if this slight covering be applied 

 close to the body, instead of reflecting back the 

 heat, it will carry it off by conduction; that is, 

 the heat will pass off through the covering closely 

 applied, and be radiated from its surface. The 

 radiation is only transferred from the tree to 



