Page:The fairy tales of science.djvu/125

Rh Those persons who dwell in dark streets and alleys are far more subject to disease than those who reside in open places. Again, those who take no heed of the old proverb about going early to bed, seldom find themselves healthy; and though they may be wealthy, they cannot be deemed wise!

Light is absolutely necessary to vegetable life, for under its influence the plant separates carbon from the air and secretes it within its tissues. Every one must have observed how plants grow towards the light, especially when confined in a room; how blanched and sickly they become in dark situations, and how speedily they recover when exposed to full sunlight. When a potato germinates in a dark cellar it puts forth long pallid shoots in quest of a stray sunbeam; but let it be exposed to the light for a few days, and these shoots will become dark and green.

Flowers are more sensitive to the influence of light than leaves; indeed almost every flower has a particular degree of light requisite for its full expansion. So regular are the periods of opening and shutting with some flowers, that they enable us to tell the hour of the day with tolerable accuracy. The great naturalist, Linnæus, made a list of no less than thirteen flowers that open and shut at different hours, and designated them by the fanciful title of "Flora's clock."

Having said enough to prove that there exists a mysterious bond of union between organization