76 GREENHOUSE CONSTRUCTION AND HEATING. 
seldom seen and never used at the present day Houses 
so constructed, with’ a maximum of woodwork and a 
minimum of glass, are totally unfit for the growth of 
tropical or exotic plants, which, when grown under such 
conditions, are always more or less long-legged, weak, 
and spindly. Then the“ numerous and too often 
unnecessarily wide ‘‘laps’’ still further exclude the 
light, especially when they become clogged with dirt 
and slime, and beyond this they admit an enormous 
quantity of the outside air, in windy weather especially, 
thus involving the waste of a large amount of heat, and 
rendering it impossible to maintain a close atmosphere, 
or any amount of atmospheric moisture in the structure. 
Houses of this kind require little or no ventilation—the 
outer air gains ingress and egress quite fast enough 
without it! 
The modern builder constructs the framework of his 
houses as lightly as possible, with comparatively few and 
thin, if somewhat deep, bars or rafters, and wide squares 
of glass. A very good and useful size for the latter is 
20in. by 16in., but for small structures the 20in. by 1éin. 
size will answer quite as well. Very large and wide 
structures, such as vineries, etc., may be advantageously 
constructed with glass as wide as 18in., or even 20in,— 
the 24in. by 18in. is now kept as a stock size by most 
glass merchants—and at least one of the large London 
market growers of pot plants, etc., builds all his houses 
with glass no less than 24in. in width. 
It is, however, a great error, whether done with a view 
of economising the woodwork, or with any other object, 
to put the glass in transversely of the bars—that is, 
