40 GREENHOUSES 



which the various members of the steel frame are riveted 

 and bolted together. The foundations of the house are 

 concrete piers extending about 3 ft. below grade, in which 

 the wrought iron rafter foot pieces are imbedded. A con- 

 crete curtain wall, 4 in. thick, is constructed on the sides, 

 and extends from a few inches below the grade to the cast 

 iron sill, which is an integral part of this mode of con- 

 struction."* 



As to the ventilation, the largest houses are now 

 fitted with very powerful cog and chain gearing, so that as 

 much as 150 ft. of sash can be parted easily by one man 

 from one point. An interesting fact about the large 

 houses is that practically the same amount of ventilation 

 appears to be sufficient for them as is necessary for the 

 smaller ones. In such gearing the lesser cog wheels are 

 contained within the oil cup and are covered in. The 

 temperature in a large house is much easier to maintain 

 uniformly than in small ones where a smaller body of air 

 is enclosed. This is an important matter in the cultivation 

 of a Sweet Pea crop. Side ventilators are necessary, and 

 at least a ventilator on the top south side should be ar- 

 ranged. 



In regard to glazing, the general practice is to adopt 

 the 16 in. x 24 in. glass. Most of the glass is either AA or 

 B glass. Very strong 29-ounce glass is necessary for the 

 larger sized pane; that is to say, the 24 in. x 24 in., and it 

 is questionable whether the increased amount of light got 

 from the larger glass compensates for the extra cost and 

 risks. Some building firms prefer the lapped form of 

 glazing rather than the butted. On this matter we express 

 no opinion, and indeed the grower who intends to build 

 will do well to consult with two or three of the greenhouse 



* Henry P. Merrick, in The Florists' Exchange. 



