440 The Principles of Fruit-growing. 
of the ground, this cold air may be drained into the 
building by means of flues which are laid through 
the walls, the outer ends standing just above the 
earth. Six-inch sewer pipes, at intervals about the 
building, answer this purpose admirably. In a build- 
ing thirty feet wide and seventy feet long, three of 
these valves along either side, and one upon either 
end, are probably sufficient for all ordinary require- 
ments. Sub-ventilation is sometimes recommended, 
and may often work to good advantage. This is 
secured by running a long pipe from near the bottom 
of a cellar storage out to the surface of the ground 
six or more rods away. This pipe has a valve at 
the outer end, or at least some protecting structure 
to prevent the leaves and litter from blowing into 
it, and it is ordinarily best, also, to have a valve 
at the inner end. Inasmuch as the earth about this 
subterranean passage is not frozen during the win- 
ter, cold air may be drawn in from the outside 
and be warmed up above the freezing point in its 
passage through the tube. This type of ventilation 
has been used with success in e¢ellars designed for 
the wintering of bees. It should always be remem- 
bered that cold air contains less moisture than warm 
air does. When very cold air is admitted, therefore, 
moisture is rapidly taken up when its temperature 
rises, and the cellar may be made too dry. It is 
advisable, therefore, to raise the temperature of such 
air to nearly its ultimate or required degree before 
it enters the storage room. 
Cellars which are very dry cause the fruit to 
