32 



VEGETABLE FORCING 



Fig. 19 shows a superior type that is used in many houses. 



Posts, purlins and braces. Iron pipe is now used al- 

 most exclusively for posts and braces, and extensively for 

 purlins. Advice regarding all details, such as size, dis- 

 tance between the posts and the arrangement of them, 

 should be obtained from the manufacturers furnishing the 

 supplies. Fig. 12 shows a properly supported and 

 well-braced house. The posts should always be set in 

 cement, to prevent the settling of the 

 house and the lifting of the roof by hard 

 winds. Angle iron, instead of pipe, is 

 sometimes used for purlins. 



Doors. The doors should be made of 

 cypress and amply large to admit carts 

 and wheelbarrows. In extensive houses, 

 at least one door should be large enough 

 to admit wagons, horse carts, plows and 

 harrows. (Fig. 20.) Double doors are 

 perhaps the most convenient and the most 

 serviceable for excluding cold. 



Glass. What is universally known as 

 "A double strength" glass is practically 

 the only kind used by greenhouse 

 builders. Although single thickness ad- 

 mits the maximum amount of light, it 

 should not be used because of the in- 

 creased breakage by hail, snow and freez- 

 ing at the laps. The glass should be clear, 

 free from imperfection and of uniform 

 thickness. 



There has been much discussion regarding the proper 

 size of greenhouse glass. Originally the panes were very 

 small, 10 x 12 inches being a popular size, but the ten- 

 dency is to use larger glass : 16 x 24 inches is by far the 



Fig. 19. A satis- 

 factory machine for 

 operating ventila- 

 tors. 



