Double- Glazing. 1 5 1 



Dr. Lindley says, " an excess of dampness is indispensable to plants, partly 

 because it prevents the action of perspiration becoming too violent, and partly 

 because, under such circumstances, a considerable quantity of aqueous food 

 is absorbed from the atmosphere in addition to that obtained by the roots." 

 In the case of great loss of vital force by perspiration, the drooping leaves 

 are so many signals calling attention to the distress ; but the loss of "aqueous 

 food " obtainable from the atmosphere is seldom, if ever, noticed. Even 

 among those who do acknowledge this source of food, many, doubtless, look 

 upon the quantity absorbed in this manner as too trifling to be worthy of 

 attention. Yet many orchids depend upon the air alone for nourishment. 

 At Chiswick, in England, a splendid specimen of Lcelia superbiens, with 

 nothing about the roots, was hung by a wire from the roof, and, under this 

 treatment, grew strongly, and flowered superbly, year after year. In such a 

 case as this, the plant being nourished entirely through the agency of the 

 air, it is absolutely essential that the atmosphere should be moist to such 

 a degree as to cause the absorption of large quantities of "aqueous food." 

 When, however, the supply of nourishment is derived in part from the earth, 

 no other source seems to claim any attention. 



But it may be said, the requisite amount of moisture may readily be 

 obtained by means of the evaporating-pans, or by syringing the floor. So 

 it may ; and the supply of" drip " will be increased just in proportion to 

 the increase in the humidity of the air, unless the glass be protected from 

 the influence of the cold from without. This protection can be given only 

 by means of mats, shutters, or some other covering ; and what covering 

 so well answers every purpose as a second glass roof.'' It is, in fact, not 

 only the best, but the oifly protection that can be used without intercepting 

 the light. 



Double-glazing, while keeping out the cold, has also the advantage of 

 keeping in the heat ; and this, added to the saving in fuel, has a tendency 

 to prevent sudden and great changes of temperature. Houses containing 

 a great amount of space are not soon heated, nor soon cooled ; but the 

 low pits in which plants generally make such vigorous growth are those that 

 need the greatest care in guarding against violent changes. For these, the 

 double roof would produce excellent results. 



Many have the opportunity of trying the system on a small scale. Sev- 



