416 The Principles of Fruit-growing 



this cold air may be drained into the building by means of 

 flues laid through the walls, the outer ends standing just 

 above the earth. Six-inch sewer pipes, at intervals about 

 the building, answer this purpose. In a building 30 feet 

 wide and 70 feet long, three of these valves along either 

 side, and one on either end, are probably sufficient for 

 all ordinary requirements. 



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 6 or more rods away. This 

 pipe has a valve at the outer end, or at least some pro- 

 tecting 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 winter, 

 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 cellars designed for the wintering of bees. It should 

 always be remembered that cold air contains less moisture 

 than does warm air. When very cold air is admitted, 

 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 nearly to 

 its ultimate or required degree before it enters the stor- 

 age-room. 



Very dry cellars cause the fruit to shrivel. Some varie- 

 ties of apples are very difficult to hold without shriveling, 

 as the Spitzenburg and the russets. Those rooms in which 

 there is a natural sand or gravel bottom ordinarily keep 

 fruit in the best condition. Cement bottoms are very 

 likely to be too dry. Running water is very often desirable 



