14 GREENHOUSE CONSTRUCTION AND HEATING. 
Beyond the three principal forms, there are a considerable 
number of others, chiefly more or less complicated, but 
those already mentioned are decidedly the most useful 
for all ordinary cultural: purposes, and with scarcely an 
exception, are employed by the large trade and market 
growers of flowers, fruit, etc. Conservatories, properly 
so called (as distinguished from houses for ‘‘ growing” 
purposes), may be, and frequently are, constructed 
in many and various ways and forms, such as square, 
sexagonal, octagonal, and even circular, with fantastically 
gabled ‘ridge and furrow,” curvilinear, and other forms 
of roof, and also with lead and other kinds of ornamental 
glazing, coloured glass, and so forth, according to the fancy 
of the proprietor or architect, or to harmonise with the 
style of the house or mansion to which they are attached. 
Such erections, though frequently highly ornamental (and 
not seldom simply hideous) are usually quite useless for 
‘‘ growing’ purposes, and in many cases if plants of certain 
kinds are kept in them for any length of time they suffer 
severely. Structures of this class are consequently briefly 
dealt with in a later chapter. 
In large market and other nurseries a number of 
span-roofed houses of the same size and character are 
frequently built side by side, so as to form a block. If, 
in such cases, side-ventilation is required, a space must be 
left, between each pair (in order to allow of the ventilators 
or sashes being opened), with separate walls to each 
structure (see Fig. 4). But where “ side-air” is un- 
necessary, aS in the case of houses intended for cucumber 
growing, etc., they may be built contiguously, the same 
wall being made to serve for a side of each, and a gutter 
