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- 
Fig. 19.—Asatis- ing atthe laps. The glass.should be clear, 
aeoriag venti, free from imperfection and of uniform 
tors: thickness. 
There has been much discussion regarding the proper 
size of greenhouse glass. Originally the panes were very 
small, 10x12 inches being a popular size, but the ten- 
dency is to use larger glass: 16 x 24 inches is by far the 
