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EXPOSURE OF PLANTS. 
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Before the general practice of bedding out and grouping in masses was adopted 
in the best gardens, it was usual to empty the greenhouse, which generally contained a 
miscellaneous, ill-assorted collection ; and about midsummer to expose nearly all its 
tenants to the influence of the air, sunshine, and rain, without hesitation or reflection. 
At the commencement of the present century, the science of gardening was little 
thought of ; persons acted by rule and routine ; hence, in less time than one fortnight 
after the turn of days, unless the season happened to be showery, and the temperature 
below its usual average, an entire collection lost all its pretensions to beauty ; the 
verdure of its foliage was exchanged for a sickly brown, and the gaiety of its bloom 
had utterly passed away. 
As philosophy and science advanced, some observant writers took up the subject 
of summer exposure. Among these we may cite the authority of Mr. Marnock, 
now curator of the Royal Botanic Garden in the Regent's Park. The following 
items will explain the writer's opinion of " The practice of turning greenhouse plants 
out of doors in summer — particularly when adopted early in the season : "— - 
" From the changeableness of our climate, and the too frequent, because often 
un-neededj use of fire-heat to guard against sudden attacks of frost, a degree of 
excitement is induced, and before the season has arrived at which they can be 
safely exposed to the open air, the plants are nearly all in a state of vigorous growth. 
In this state they are at once removed to summer quarters, when, although the 
frosty nights may have gone by, the temperature is often so low that a complete 
check is given, from which they seldom recover till toward the approach of autumn ; 
when, after having regained their energy and become inured to their new climate, 
they make a new effort to grow." 
Mr. Marnock is right ; but he has not taken into account the peculiar agency of 
full solar light, undiluted (if the expression be permitted) by the agency of refraction, 
which had operated so decidedly through the interposed medium of a crown-glass 
roof. A Fig Tree in the highest state of verdure was once removed to the open 
air from a temperate stove. In a few hours every leaf was paralysed, and the entire 
foliage fell off. This afforded one ocular proof, among many others, of the injury 
which plants sustain from a sudden and direct exposure to the sunbeams, and also 
to the violence of unintercepted currents of wind. 
" Orange Trees, Camellias, and, indeed, all plants with coriaceous, or thick, 
fleshy leaves, are, from a variety of causes, liable to be injured by the sun ; but this 
injury would seldom occur were they retained in the house both summer and winter, 
and kept as cool as possible during the latter season. Consistently with the above 
considerations fire-heat need never be applied till the thermometer in the house has 
indicated three or four degrees of frost." 
The untempered solar heat, it may be added, arrests transpiration, and injures 
VOL. XV. NO. CLXXVI. A A 
