PROTECTION OF PLANT-HOUSES DURING COLD NIGHTS. 315 



We have instituted numerous experiments with the view of 

 ascertaining the capacity of various substances for the protection 

 of plants and horticultural structures, by which we find that 

 bodies of soft and open texture, — as woollen netting, thin cloth, 

 &c., — will, on dry, clear nights, afford an amount of protection 

 equal to 7° of frost. But if the covering should become wet 

 before the frost sets in, it will afford very little protection to the 

 plants beneath it. 



Coarse cloth, which had been coated with paint, kept out 10'^ 

 of frost, and several kinds of plants, which, at the freezing point, 

 would suffer injurj-, were kept alive during the whole winter, 

 with the thermometer occasionally indicating 22^ of frost. These 

 plants were frequently frozen, but the covering was never removed 

 during several months, although the air circulated freely under- 

 neath the glass. 



In protecting plants, or glazed structures of any description, it 

 is essential to observe that the covering should always be placed 

 so that a stratum of air may always be confined between the 

 covering and the objects to be protected ; this is an important 

 part of he matter, as, if the covering be laid immediately on the 

 glass of a frame, or green-house, which it is wished to protect, 

 the cold will be conducted by the covering to the glass, which 

 in turn will cool the air beneath it. The covering should never 

 touch the object to be sheltered, though, from what we see around 

 us, this point appears to be very little attended to. 



A covering of thin cloth, or woollen netting, when suspended 

 in a vertical position over trees, &;c., will afford better protection 

 than the same substance laid horizontally over the surface. In 

 this manner, wall trees are protected in the British Isles from 

 spring frosts, and we have frequently seen the blossoms of peach, 

 apricot, and pear trees completely uninjured under woollen or 

 hair netting, when the hardiest trees of the woods were nipt 

 with frost, and the tender vegetables of the garden were entirely 



smaller fibers of the roots, with a view to watch the progress of the for- 

 ination of new ones. At the end of a fortnight he had the plants all 

 taken up and examined, with all possible care, to prevent injuring them, 

 and found that, when they did not actually freeze, new roots were alwav.s 

 uniformly developed. 



