PITCH OF ROOF. 29 
roof, leaving the lower part cool. The temperature in 
such structures is consequently much more even and regular 
—a most important matter in the successful culture of many 
kinds of plants. On the other hand, plants of low growth 
must stand at a considerable distance trom the glass in such 
large structures, and this is usually considered by most 
growers to be a disadvantage, but if so constructed as to 
admit a maximum of light, and at the same time freely 
ventilated, it will be found that plants will not, as a rule, 
become ‘‘ drawn” or ‘‘run up” to nearly the same extent 
in such houses, even when standing far from the glass, as 
they would do under similar conditions in smaller structures 
—that is to say, provided that they are not unduly crowded. 
Again, plants growing far from the glass, in spacious 
houses, will neither become scorched or “scalded” in 
sudden bursts of strong sunshine as they are very liable to 
do in small ones, especially if air is not given promptly, nor 
are they so likely to suffer from frost in cold weather as 
they would be if standing closer to the glass. On a sharp 
night, it is those nearest the glass that ave ‘‘ nipped ” first— 
and worst. 
Lastly, large houses may be heated to and kept at the 
same temperature with less piping, proportionately, and 
consequently with less fuel, than small ones, the radiating 
surface being smaller in proportion to the cubic contents. 
Pitch.—The pitch of roof next demands consideration. 
Generally speaking, greenhouses of all kinds are now 
constructed with flatter or lower-pitched roofs than they 
were a quarter or half a century ago. In a structure with 
a high pitched roof the upward current of air, when the 
roof ventilators are open, is much sharper than in a low or 
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