The Garden Under Glass

CHAPTER XXVII VENTILATING, HARDENING OFF AND SHADING The Principles of Ventilation It will, I think, be readily understood that the art of ventilation of glass houses, used for the cultivation of fruit and plants, is a matter of supreme importance in the curriculum of culture. Glass has this peculiarity when formed into an enclosed structure, that while it readily admits the light and heat of the sun, it stops radiation or m other words, it does not allow the heat to readily escape' This is a great advantage, for by this means the heat of the sun may be bottled up for a considerable time, and the næd for fire-heat is either done away with or considerably diminished. It may, however, happen that all the heat gained in this way is not required, and the only method of regulating the quantity is to reduce it by opening the house at the apex to admit of its gradual escape. Apart also from the maintenance or reduction of the temperature it must be a well-known faet that plants need a supply of fresh aii, and they should always have as miich as can be afforded without reducing the temperature below the minimum at which the plants are known to succeed. It is this fear of giving too mueh air which causes stagnation of the atmosphere and militates strongly against good culture, because the plants have nothing to induce them to expand. For plant life as for human beings a movement in favour of more fresh air is sadly needed. 261