66 THE PRINCIPLES OF FLORICULTURE 



the possibility of moisture-collecting joints, and with fre- 

 quent and careful applications of paint, all-wood houses 

 will last a considerable period. The framework must, of 

 necessity, be of larger dimensions than when iron is used, 

 therefore light conditions are not the best. 



In selecting material for construction, a light, strong, 

 straight-grained, durable wood allowing of small dimen- 

 sions should be used for the superstructure. Wood with 

 the grain running diagonally is much weaker than wood 

 with a straight grain. White and yellow pine are fre- 

 quently used, but they are not equal in value to cypress 

 or redwood. Fortunately the supply of these is sufficient 

 to meet the demand at the present time, but with a 

 diminished output and more and larger greenhouses con- 

 structed each year, there will eventually be a scarcity of 

 cypress and a demand will come for other durable woods. 



58. Semi-iron houses. The methods of combining 

 iron and wood for construction purposes are many and 

 varied. Each firm of greenhouse builders has its own 

 particular method which, in its opinion, is far superior 

 to any other. 



Flat-rafter sectional houses (Fig. 9) . In flat-rafter 

 sectional houses, a combined steel side-post and roof- 

 rafter, three inches wide by one-fourth inch thick, extends 

 from a foot-piece which is firmly embedded in concrete, or 

 from an iron sill which is laid on a concrete wall, to the 

 eaves and ridge of the houses. These posts and rafters 

 are placed eight feet four inches apart, and these sections 

 may be extended indefinitely by removing the end parti- 

 tions in the houses. Purlins of angle-iron extend from 

 rafter to rafter and are held in place by iron lugs. Each 

 rafter is capped with a narrow, wooden sash-bar, and be- 

 cause of the strength of rafters and purlins, all sash-bars 



