74 PLANT PROPAGATION 
should be used in the construction of the roof, for wood 
is the best insulator, while iron, with its conductive 
properties, is too easily affected by atmospheric in- 
fluences. A few ventilators must be made on each side 
of the roof. In propagating-houses air is very seldom 
-admitted at the bottom on account of all the heat being 
wanted for the propagating-beds. 
It is preferable to have, as shown in the illustration, 
some hollow stages which can be closed up by the planks 
G, G. These can easily be made in lengths of several 
feet, and can be removed if not wanted. Slates should 
be used in the making of the stages, and no cement 
joints must be allowed. Water should drain through 
quite easily, and the heat also pass through readily to 
warm the propagating-beds (C, C), which may be 
composed of sand, coconut-fibre, sawdust, etc. 
The frames (A, A) can also be easily made. Two long 
planks are required, one 13 foot wide on the back, and 
the other 14 foot on the front. They must be fixed one 
to the walls and the other to the stage, and between 
each light a transverse piece of wood will divide the two 
sides. The lights (B, B) are only placed on the frame, 
and, if they have to be removed, they can be fastened 
with the hooks (I, I) in the rings (i, i) on the front of 
the lights. During the summer, if they are not required, 
they can be removed altogether. A top or hanging shelf 
(H) has been drawn above the path, leaving 6 feet 
6 inches. No side shelf could very well be fixed, 
owing to the lights, which are constantly being moved 
up and down. This shelf is of very great use, chiefly 
for pans or boxes containing plants in the course of 
propagation, and requiring to be placed as close as 
possible to the glass. Seedlings are successfully raised 
