| Green-leaved plants need light to live. Light acting | | | | flowering plants, such as African violets, gloxinias, |
| upon leaf and stem cells helps change carbon | | | | other gesneriads, and foliage plants, thrive under |
| dioxide taken from the air and moisture from the | | | | artificial light. The addition of fluorescent or |
| soil into sugars and starches, necessary elements | | | | incandescent light, or a combination of these, can |
| for plant growth. This manufacturing process is | | | | convert dark, wasted space under benches and |
| called photosynthesis. To carry on photosynthesis | | | | on window-less wall areas, as well as in |
| plants must have, in addition to light, proper | | | | basements and closets, into profitable |
| temperatures and nutrients. | | | | plant-growing space. |
| Measuring Light | | | | Some greenhouse owners have found that |
| Light is measured in foot-candles. One foot-candle | | | | fluorescent light speeds propagation and flowering |
| is "the illumination at all points that are 1 foot from | | | | of African violets, so they grow the plants in a |
| a uniform source of 1 candle-power of light. "The | | | | combination of natural and artificial light. |
| intensity of light varies with the seasons. In | | | | Day Length |
| summer, it may reach 10,000 foot-candles or | | | | The growth and flowering of many plants depend |
| more during the brightest part of the day. This is | | | | on their daily hours of exposure to light-either |
| too much light for African violets, begonias, and | | | | natural or artificial. Without going into technical |
| decorative green pot plants. During winter months, | | | | detail, this, roughly, is called photoperiodism, a |
| light intensity may be reduced to a meager 500 | | | | phase of which is called day length. Plants are |
| foot-candles. Clouds and smoke from factories | | | | informally classified into three groups. |
| also reduce light. | | | | 1. Dahlias, delphinium, pansies, tuberous begonias, |
| When light intensity becomes too low, plant | | | | and other plants which come into flower more |
| growth slows almost to a halt, stems become | | | | rapidly during the long summer days of maximum |
| weak, leaves thin, and flowers are paler than | | | | light-or under the stimulus of artificial lighting-are |
| under normal conditions. Under too-high light | | | | called long-day plants. |
| intensity, plants tend to wilt, wither, and may | | | | 2. Chrysanthemums, gardenias, poinsettias, etc., |
| become yellowed or show burned spots. | | | | which start to flower when their light-exposure |
| With optimum conditions such as good soil, | | | | period goes down, are called short-day plants. |
| correct watering, and proper temperatures, food | | | | 3. A third group contains plants-including African |
| production in plants is stepped up as they receive | | | | violets, carnations, and roses-which are unaffected |
| more light. To achieve maximum growth and | | | | by day length; these are called indifferent. |
| flowering, you must regulate light intensity to | | | | Science is now trying to determine whether plant |
| make up for seasonal changes. Shade your | | | | growth and flowering are actually governed more |
| greenhouse during summer to cut down the light; | | | | by the daily period of uninterrupted darkness than |
| remove shade to admit more winter sun; brighten | | | | by the length of exposure to light. Thus the plants |
| all dark corners with artificial light. | | | | that are now classed as long-day and short-day |
| Artificial Light | | | | eventually may be called short-night and long-night |
| Given proper temperature and humidity, many | | | | plants. |