16 THE FORCING GARDEN. 
and additional influence upon everything exposed to 
it, when wet or damp more than when it is dry. The 
practical man will know at once how to appreciate the 
double glazing above the single, on account of the 
under glazing being preserved dry, which no single 
method can do. 
Single glazing may be employed for all cool 
orchard houses, vineries, cool plant houses, &c.; but 
I recommend all forcing houses and tender exotic 
plant houses to be double-glazed on one of the plans 
illustrated and described in this work. 
