Ventilation of greenhouses

2062. Air is supplied by the portion of the atmosphere enclosed in the structure. This air may be raised in temperature, charged with vapours, or renewed, at the will of the operator. It might also be put in motion by art, for the sake of obtaining strength of stem in ramose or tree-like plants; but the motion communicated to plants, by opening the cover, and exposing them to the direct influence of the air in fine weather, is deemed sufficient, either for this purpose, or for giving flavour to fruits when advancing to maturity.