sliding shutters, and would communicate internally with a chamber (_g_) formed between the front wall and the side of the tank; this chamber would also communicate, by a series of openings, (_h_) with the interior space above the water in the tank, and from this space, through the covering of the tank, tubes (_m_), also placed at intervals, would be carried up through the soil, close to the side of the wall; these tubes should be furnished with caps or valves, so as so admit of the communication being stopped at any time. In applying this to the admission of air, we must not loose sight of a series of ventilators, (_i_), placed in the back wall of the house, which are of precisely the same nature and construction as the apertures (_f_), already spoken of. I shall have occasion hereafter, to notice the admission of air, but it will be well in this place, to explain the action of the plan proposed for that purpose: when it is judged that a change of the internal volume of air is requisite, the ventilators (_i_) are to be opened, which admits of a portion of the rarified air to pass off; the ventilators (_f_) are also to be opened, and by means of the action of these ventilators on each other, a portion of external air is taken in; this enters the chamber (_g_), which is warmed by its contiguity to the tank, and here becomes partially rarified, and rises to the top of the chamber; the apertures (_h_) admit it to the interior of the tank, where it becomes not only thoroughly warmed, but also imbibes a degree of moisture proportionate to the degree in which it becomes heated, and thence it enters the house by the tubes or shafts already spoken of. The advantages of warming and moistening the air thus admitted, are very important ones; for when either a cold or dry state, of the atmosphere prevails, its influence is very injurious to plants in these confined situations: cold raw air, when it comes in contact with the tender foliage of the plants, has the effect of chilling the sap in its progress through their tissue, and thus lessening their excitability, when it should be increased; whilst dry air acts as an incessant drain upon the vegetable juices, which it abstracts through the stomates and pores of the leaves and stems. When cold air is admitted to any position where it can unite with caloric, and not in an equal ratio with moisture, it necessarily becomes arid, and in that state it eagerly combines with moisture in any form with which it can come in contact therewith; and consequently if cold air is admitted to a plant structure, where it can have the means of combining with heat, faster than with moisture, it would be brought into this arid state, and would supply its voracious appetite, by abstracting the juices of the plant. It is a very important question how far this state of things is connected with many of the diseases as they are called, to which plants are subject; for my own part, I believe it to have a very