i8 THE UNHEATED GREENHOUSE 



successful culture ; but in an unheated house moist air, which 

 in winter is liable to be stagnant and must be chill, is exactly 

 what we have to avoid. To put it more accurately, we must 

 have it in our power to regulate the degree of atmospheric 

 damp, supplying moisture when required in hot, dry weather, 

 but keeping mostly on the side of moderate dryness both in 

 summer and winter. Where the roof is steep, however, hot 

 sunshine will cause a rapid upward current, which dries the 

 air so thoroughly that plants will quickly droop, and unless 

 constantly refreshed they will soon hang out signals of supreme 

 distress in the way of blight. Not only so, but a steep roof 

 takes more glass and presents a greater surface to frost. A 

 happy mean must therefore be struck, and it lies between the 

 two extremes of 25 and 35, or at most 40, with the proviso 

 that the house be kept as low as it reasonably can be in 

 accordance with its proposed purpose, whether it be for 

 dwarf-growing alpines or flowering shrubs or Roses. For a 

 small house 20 ft. by 12 ft., a good average slope would be 

 37, for if the width be narrow a higher pitch is required to 

 give standing room ; but in planning a house it is much 

 better to allow for as much breadth as possible, as it will be 

 found more convenient in every way. 



Careful glazing is essential. Glass of 2 1 oz. quality should 

 always be used, to save breakage amongst other reasons, and 

 a good average size for the panes is 22 in. by 14 in. 



It was pleaded not long ago in a monthly serial of high 

 artistic authority that greenhouses should be built "as of 

 old, with small sheets of glass laid thickly overlapping, and 

 more proof against scorching and freezing than the neat, big- 

 sheeted, modern kinds," and from an artistic point of view 

 this advice cannot be gainsaid. There is truth, too, in the 

 argument that thick overlapping may give more shade in 

 summer and greater protection in winter, though it does not 

 counterbalance other disadvantages; but greenhouses, un- 



