NOTES ON WINTER GARDENING. 91 



suggested that these purlins be utilized in conducting steam for 

 heating, but the advisability of such a practice is questionable 

 because of the alternate contraction and expansion which would 

 follow and the consequent disturbance of the glass. Each sash 

 bar is held in place by means of an iron strap. 



A ridge pole of 2x5 stuff is generally used. This should be 

 grooved at the sides to receive the glass, as shown in the figure. 



c. Glass: — In general it is better to get second quality double 

 thick glass of pretty good size. We prefer 14x22 or 16x24 

 although because of the lower price on smaller sizes it is com- 

 mon among florists to use 12x15, this being the largest size at 

 the low prices. Belgian glass is more expensive than the 

 American product but is superior to the latter. In some sec- 

 tions heavy plate glass is employed. Of course this latter is 

 very expensive, but it is very durable. 



There is a common notion that a flaw or bubble in the glass 

 is likely to serve as a lens and result in burning foliage. Such, 

 however, is not the case as was shown by some very careful work 

 conducted by Mr. J. C. Blair at Cornell University during the 

 past year; but glass of a wavy character or of uneven thickness 

 should be discarded. It is glass of this character that causes 

 the trouble. 



5. Ventilating and Ventilating Machines. 



In general, ample provision should be made for ventilation. 

 The object of ventilation is to purify the atmosphere rather 

 than to lower the temperature and provision should be made 

 whereby the outside air may be admitted near the base of the 

 house as well as at the ridge. The ventilators should extend 

 the whole length of the house, rather than be confined to a 

 few small sashes. It is better to raise the whole line a little 

 than to raise a few sashes to a greater extent, as in the latter 

 case there is danger of injury from cold drafts. Many growers 

 prefer that the ventilators should spring from the ridge, as in 

 this way the warmest air will escape and it is claimed that the 

 house may be kept cooler in very hot weather. In our own 

 experience, however, we prefer to have two lines of ventilators 

 operated independently. In this way, provided the ventilators 

 are hinged at the ridge, we may avoid direct drafts in case of 



