The principle involved in the plan proposed for aëration or ventilation, is no doubt a sound one; and though the plan which is more particularly described may be modified and varied, yet it is believed to be efficient for its intended purpose.
There can be no doubt that the admission of cold air to a structure in which tender plants are being forced, either during winter or early spring, is materially hurtful to the plants, in proportion to the tenderness of their constitution; and the Cucumber being, under those circumstances, a plant of a very tender and delicate nature, is especially susceptible of harm from this source. As a consequence resulting from this fact, there can be little hesitation in affirming that whatever fresh or external air it may be necessary to admit, during the period referred to, should be warmed before it reaches the plants, and in being warmed not burned, but supplied with the additional moisture its increased heat capacitates it to take up, and which, to be congenial to vegetation, it requires. This is provided for by the plan already recommended, where the cold air is made to pass through the tank containing the heated water which warms the soil. By a perfectly practicable modification of this arrangement, not only may this result be secured, but also the continual circulation of the internal atmosphere may at pleasure be assisted and accelerated, during the time when it might not be necessary to admit fresh air. This would be an additional advantage. The arrangement proposed to effect this, is to conduct the cold external air through a heated chamber containing the tanks--these latter being covered, but also admitting of being opened to any extent to supply moisture or steam in the proportion required. The cold air, after passing upwards through the chamber, escapes at the front of the house, and ascends to the upper part of the house, from whence it finds its way downwards near the back wall, and there again enters the chamber, through openings provided for the purpose. The circulation of the internal atmosphere would be thus facilitated and accelerated, even without the admission of any current of external air, for, of course, there is more or less of this kind of movement going on in the atmosphere, wherever and in whatever form a source of artificial heat 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."