2151. The evil effects of the sudden admission of cool air into a heated hothouse were very great. The usual mode of lowering the temperature was by opening the sashes in front, and those in the upper part of the roof at the same time, and thus placing the plants in a thorough draught. In addition to this, it was found that 'when the external air enters a hothouse in which the air is at a high temperature, it rushes in with considerable velocity, driving out by the pressure of the atmosphere the hot and vaporous air by which the plants are surrounded, and becoming heated and charged with moisture at the expense of the earth in the pots, and the foliage of the plants.' (Loudon's Horticulturist, p. 85.)
