OF PLANTS AND PLANT-HOUSES. 
207 
The disciples of the theory promulgated by Mr. Ward, in whose air-tight glass 
cases plants such as Cacti, Orchids, Ferns, and other Cryptogams, managed to drag 
out an enfeebled existence for many months, ran away with the idea some years 
back, that because these plants lived, other plants must grow, and consequently 
ventilation became a very secondary consideration among scientific men ; indeed, we 
recollect a range of houses, the top sashes of which were all screwed down, and the 
result was, the black Hambro' Grapes became red ones in succeeding years, and the 
gardener lost his situation. To these houses air was admitted by holes cut midway 
between the glass and the footpath of the house in the back wall ; but these holes 
we never reopened, except to lower the temperature of the house. Horticultural 
architects, who too frequently know nothing of practical gardening, soon took up the 
idea, because it was fashionable ; and hence it would be easy to point to iron-roofed 
houses built about that time, which were so badly ventilated, as to render it 
impossible, without shading in sunny weather, to prevent the plants being 
scorched to death. This was one of the reasons why metallic-roofed houses became 
so unpopular, and were so much dreaded by professional men. 
We have always laid it down as a rule, that plant and forcing-houses should 
never be closed during either night or day except in the most severe weather, but 
that " from night to morn, from morn to dewy eve," there should be a constant and 
perpetual interchange of the external and internal atmospheres. While, however, 
we would do everything in our power to secure this interchange, there are one or two 
things which must be carefully guarded against. We all know how very injurious it 
is to the animal frame to be placed in a current or draught, and that a current of 
air admitted through a broken window will lay the foundation of diseases which will 
quickly gather a strong man to his fathers. Scarcely less injurious are currents of 
air to plants, no matter whether they be warm or cold ; and there are certain green- 
house plants — as, for illustration, Boronia serrulata and pinnata, Crowea saligna, 
the whole tribe of Gompholohiwns, and many other Swan Eiver and New Holland 
plants — which, if placed in a current, will not only refuse to grow, but will positively 
die. Even Heaths hate a current such as is admitted by the small opening of a 
sash, but they delight in a free circulation of air, admitted in a volume, so as to act 
upon the whole plant at the same time. No greater proof can be given of the inju- 
rious tendency of currents of air to plants, than the fact, that a current of frosty air 
admitted through a broken square will kill a plant in a greenhouse, the temperature 
of which shall never be below the freezing point, while the same plant, though frozen 
quite hard, but protected from a current, would be uninjured. This fact we proved 
, several times during the last severe winter, and so satisfactory was it to us, that 
while we admit all the air we can to our plant-houses, we always take care to guard 
against strong currents. 
From the preceding remarks it will be seen that the ventilation of plant- houses 
is an operation which requires careful management, and is a point in cultivation 
which it is necessary should be well studied. In congenial weather, of course, air 
