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top of the chamber ; the apertures (A.) admit it to the 

 interior of the tank, where it becomes not only thoroughly 

 warmed, but also imbibes a degree of moisture propor- 

 tionate 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 vegeta- 

 ble 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 impor- 

 tant 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 considerable influenee in the production of many 

 of them. A shallow bed of soil (k), is all that would be 

 required; for in the winter season, there is nothing 

 gained by encouraging a very luxuriant and gross state of 

 growth : the composition of this soil will be noticed 

 hereafter: beneath it, and resting on the top of the 

 tank, should be placed a layer of coarse open rubble, not 

 less than six inches in thickness ; and amorfg this rubble 

 c 



