Question

Greenhouse, also called glasshouse, building designed for the protection of tender or out-ofseason

plants against excessive cold or heat. In the
17th century, greenhouses were ordinary brick or
timber shelters with a normal proportion of window
space and some means of heating. As glass
became cheaper and as more sophisticated forms
of heating became available, the greenhouse
evolved into a roofed and walled structure built of
glass with a minimal wooden or metal skeleton. By
the middle of the 19th century, the greenhouse had
developed from a mere refuge from a hostile
climate into a controlled environment, adapted to
the needs of particular plants. A huge increase in the
availability of exotic plants in the 19th century led to
a vast increase in glasshouse culture in England and
elsewhere. Large greenhouses are important in
agriculture and horticulture and for botanical
science, while smaller structures are commonly
used by hobbyists, collectors, and home gardeners.
The modern greenhouse is usually a glass- or
plastic-enclosed framed structure that is used for
the production of fruits, vegetables, flowers, and any
other plants that require special conditions of
temperature. The basic structural forms are the
span-type greenhouse, which has a double-sloped,
or A-shaped roof, and the lean-to greenhouse, which
has only one roof slope and leans against the side
of a building. Two or more span-type greenhouses
are sometimes joined side by side so that they have
fewer external walls, and heating costs are
consequently less. A greenhouse has a large
expanse of glazing on its sides and roof so that the
plants are exposed to natural light for much of the
day. Glass has been the traditional glazing material,
but plastic films, such as polyethylene or polyvinyl,
and fibreglass are also common. The framing of the
structure is made of aluminum, galvanized steel, or
such woods as redwood, cedar, or cypress. A
greenhouse is heated partly by the rays of the Sun
and partly by artificial means, such as circulating
steam, hot water, or hot air. Because a greenhouse
can become too hot as well as too cold, some type
of ventilating system is also needed; this usually
consists of roof openings, which can be operated
mechanically or automatically, and end-wall
openings, through which electric fans draw air and
circulate it throughout the interior.
The plants grown in greenhouses fall into several
broad categories based on their temperature
requirements during nighttime hours. In a cool
greenhouse, the nighttime temperature falls to
about 7–10°C (45–50°F). Among the plants suited
to cool greenhouses are azaleas, cinerarias,
cyclamens, carnations, fuchsias, geraniums, sweet
peas, snapdragons, and a variety of bulbous plants
including daffodils, irises, tulips, hyacinths, and
narcissi. A warm greenhouse has nighttime
temperatures of 10–13°C (50–55°F). Begonias,
gloxinias, African violets, chrysanthemums, orchids,
roses, coleuses, and many kinds of ferns and cacti
and other succulents are suited to such
temperatures. In a tropical greenhouse, or
hothouse, which has nighttime temperatures of 16–
21°C (60–70°F), caladiums, philodendrons,
gardenias, poinsettias, bougainvilleas,
passionflowers, and many kinds of palms and
orchids can be grown. In countries with cool
climates, commercial greenhouses are used to
grow tomatoes and other warm-weather
vegetables.
Available a

A greenhouse:
a) is a kind of house built of plants.
b) is a mere refuge from wild animals.
c) is a controlled environment, adapted to the
needs of particular plants.
d) is a plastic house for living which was created
as a sustainable way of life.
e) is a cold refuge to protect animals and plants
from the Greenhouse Effect.

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