Greenhouses vary as much in style and cost as dwellings. The simplest is any tight enclosure, covered with a glass roof at an angle of forty-five degrees, facing the south, and kept warm by artificial heat. The temperature is not allowed to be lower than forty nor higher than seventy degrees of Fahrenheit; this will keep plants growing and make them blossom, and affords a good place for starting plants to be transplanted to out-door hotbeds, and finally to the vegetable garden, after frosts are over. There is but one main danger in greenhouse culture, and that is obviated by a little care: it is, allowing the air to become too much heated for the health of the plants; they require but little heat, but need it regularly. Some greenhouses are warmed by stoves, and serve a good purpose; others have a stove set in a flue which is built in the wall, gradually rising until it has passed around two or three sides of the building. Place three or four sheet-iron pans over this flue, at different points, and keep them filled with water; the fire in the flue will heat the water, and impart both warmth and humidity to the atmosphere, which is very favorable to the health and growth of plants. Such a house is favorable to the growth of tender exotic fruits and plants. A similar house without any artificial heat affords an excellent place for the cultivation of the finest varieties of foreign grapes. GYPSUM, OR PLASTER OF PARIS. The fertilizing properties of this article were discovered by a German laborer in a quarry, who observed the increased luxuriance of the grass by his path, when the dust fell from his shoes and clothes. This led to experiments which demonstrated its fertilizing power. With the protracted controversies on gypsum we have nothing to do; certain important facts are established which are valuable to agriculturists.