858 PROTECTION FROM ATMOSPHERICAL INJURIES. 



forming for such plants artificial climates, as in the different kinds 

 of hotbeds and hothouses ; but there are also various contrivances for 

 protecting plants growing in the open air or against walls, and it is to 

 these that we at present intend to confine our attention. They may 

 be included under shading from the sun, sheltering from wind, and 

 protecting from rain or from cold. 



The object of shading is to lessen evaporation from the soil or from 

 plants, or to exclude light or heat. It is effected by interposing some 

 opaque medium, or glass, the purest of which, as we have seen, excludes 

 a certain portion of light, between the objects to be shaded and the 

 direct rays of the sun, and this medium differs in its texture and other 

 properties according as it is intended to be temporary or permanent. 

 Mats and canvas are the common articles for temporary shading in the 

 case of plants under glass ; but for plants in the open garden, hurdles of 

 wickerwork, or frames filled in with beech or birch branches, or screens 

 of reeds are used, or the plants are placed on the north, east, or west 

 sides of walls or hedges. Sometimes also they are planted under 

 trees : but as this kind of shade excludes rain and dew, it is only adopted 

 in particular cases. A slight degree of shade is produced by form- 

 ing the surface, of ground into narrow ridges in the direction of east 

 and west, and sowing or planting the crop on the north side of the 

 ridge. On the same principle, crops in rows in an advanced state are 

 made to shade seedling crops sown between them, when shading them 

 is desirable. Oil paper-caps, and other articles for shading individual 

 plants have been figured and described, and also canvas shades for hot- 

 house roofs. Some of the most severe injuries which plants trained 

 against walls sustain in this country are from the powerful action 

 of the sun in early spring, succeeded by extreme cold ; but by 

 judicious shading such evils may be greatly mitigated or altogether 

 avoided. 



Sheltering from wind, the principles of which have been pointed 

 out, is effected on a large scale by plantations, and in gardens by 

 walls, hedges, hurdles, wickerwork covers, hand-glasses, cloches, move- 

 able frames, and other articles. 



The principles of protecting from cold have been described at length 

 in our chapter on the atmosphere, and the different materials and con- 

 trivances for this purpose have been enumerated. Coverings for the 

 surface of the ground include dead leaves, litter, straw, sawdust, spent 

 tan, rotten dung, coal ashes, coarse sand, spray and branches of trees 

 or shrubs, &c. Coverings for standard plants in the open garden in- 

 clude temporary roofs of thatch, boards, canvas, wickerwork, bark, or 

 manufactured materials, such as pitched paper, asphalte sheeting, &c. 

 Coverings for walks include glass, branches with the leaves on, such as 

 those of the silver or spruce -fir, of the beech, birch, or hornbeam, 

 cut before the wood is ripened, in consequence of which the leaves 

 will adhere to the shoots, and being dead and without moisture, they 

 are better non-conductors than green leaves, straw or hay ropes, rope- 

 netting, canvas, bunting, woollen-netting, oiled paper-frames, wicker- 

 work, hurdles, &c. 



