at
is present. Another mode of combining internal atmospheric motion, with
ventilation, and by which the cold air is warmed before it reaches the
plants, has been practised with very marked success, in a vinery at
Park-hill, Streatham, Surrey; and I have described it in the _Journal of
the Horticultural Society_[1] as follows:--"This plan consists in passing
a zinc pipe, thickly perforated with small holes, from end to end of the
vinery, and exactly beneath the range of hot water pipes, which heat the
structure. In the outer [end] wall, communicating with this perforated
pipe by means of a kind of broad funnel, a register valve is fixed, by
which the admission of air can be regulated with the utmost nicety, or the
supply be shut off altogether: this valve is fixed a little below the
level of the perforated pipe. The action of this contrivance was evident
enough from the motion communicated to the foliage of the vines; and its
effects were apparent in the unusually healthy and vigorous appearance
they bore, until their period of ripening. In this case, sufficient
moisture was kept up by syringing the walls and pipes, wetting the
pathway, and by the use of evaporating troughs, placed on the metal pipes,
and kept constantly filled with water."

In another communication published in the work already quoted,[2] after
alluding to the now well-known garden truism, that a comparatively low
night temperature is indispensable to the maintenance of vigorous growth
in plants of all kinds, I have advocated a more extended adoption of the
practice of night covering hot houses, as a means of permitting the low
night temperature required, and at the same time securing the plants
against the extreme cold to which they would thus be sometimes liable.
From the changeable nature of our climate, there is some difficulty in
apportioning the degree of applied heat, so as to suit exactly the
requirements of the plants in these respects; and it is especially
difficult to maintain with certainty the low degree of night temperature
which would be desirable, and at the same time avoid risking the safety of
the plants, through a sudden declension of the temperature of the exterior
air. At present this difficulty has to be met by extraordinary care on the
part of the gardener, and often by serious encroachments on his proper
time for study and for rest: even then sometimes without success. This end
would be much more effectually and certainly secured