84 GREENHOUSE CONSTRUCTION AND HEATING. 
though as a rule they are cast simply with shoes at the 
base to fit on to and be secured to the bottom plate with 
screws or bolts. They may also be cast with lugs on the 
upper ends to which brackets to carry the lower ends of 
the rafters may be bolted, or simply with shoes cast on, 
to receive the latter. Lugs are also frequently cast on 
them to which the ends of the JT irons which carry the 
wires in vineries and cucumber houses may be bolted. 
Cast-iron spandrils are frequently employed in the 
construction of span-roofs, whether principal rafters are 
used or not. These not only secure the rafters at the 
proper angle, but have 
a very light and orna- 
mental appearance 
also; if sufficiently 
large, they, to a 
great extent, dispense 
with the necessity for 
Fic. 64: tie-rods_ across the 
roof, unless the rafters are of great length, and lastly, 
they afford more head-room in small structures than if 
tie-rods were employed (see Fig. 64). At the same time 
these last, if made of stout bar-iron, are very useful to 
carry shelves upon, where there is enough head-room 
beneath to move about comfortably-- 
Standards should always consist of iron, if possible, as 
wooden ones have a very heavy appearance. In 
nurserymen’s structures they frequently consist simply 
of a length of ordinary ldin. or 1ldin. gas-barrel, but in 
large conservatories, palm-houses, etc., cast-iron columns 
are employed to support the roof. 
