PLANTS, EFFECT OF AIR AND LIGHT ON. White is said to be no color at all. It is, however, tangible enough to our sense of sight. It would seem to be the primary color, because the so-called decolorization of a substance results in white. Air and water, in a fluid state, are colorless, but they reflect any color that may be placed against them. Frozen water—pounded ice and snow—however, becomes white from its power of reflecting that color. One of the effects of air and light upon plants, is to cause theta to change color. The embryo plant, as formed within its integuments, is usually white or nearly so, and a plant, colored by contact with light and air, may usually be blanched by shutting out the light, the blanching being perfect or otherwise, according to the thoroughness with which the light is excluded from the Thus, in blanching celery, it is covered with earth to such a depth as to entirely shut out the light when it becomes thoroughly white, and also crisp. Lettuce or endive, however, is 'blanched by tying the leaves together, and is only partially blanched and crisped, for, it is blanched only in proportion to the quantity of light excluded. But some plants—such as rhubarb—develop color although grown in the dark, but this is from the pre-existence of color in the root from whence the stalk sprang. Or the deposition of coloring matter may take place as in some varieties of potatoes, beets, carrots, etc., being first formed by parts developed in the light. Flavor, as well as color and nutritive matter, is dependent also upon light for its pre sence, because flavor is produced by chemical Alterations, caused by the exposure of the plant to the light. A very curious fact connected with this, is that the portion of a fruit, as a water melon, shielded from the light, will not be as sweet as that portion receiving the full effect of light. It will also be remarkably retarded in the development of saccharine matter, from the absence of light and heat. Hence gardeners sometimes place slates or some other conductor beneath such fruits as they wish to be .very fine and well developed. On the other hand, the sugar-beet is remarkably deficient in saccharine development in that portion growing above ground, and contains instead certain salts, which neutralize, partially in the manufacture of them, the saccharine contained in the portion below.
i It is a curious fact, and well worthy the inves of agricultural scientists, from the pos sibilities which may be wrought out from its study. Light is also indispensable to the develop ment of the nutritive matter which is formed by the exposure of the leaves to the light. Thus the potato, when forced in the dark, is said to contain no more farinaceous matter than was contained in the original tuber, and it is also a well known fact that fruits grown in illy-lighted and unventilated houses, are innutritious and flavorless. Light being so powerful a stimulus in vegetative economy, its energy in exciting the vital action of plants is in direct proportion to its intensity, hence the superior quality of fruits grown in a sunny and equable climate like Califor nia over those cultivated in less favored zones. So
also the intensity of color in the leaves of a plant is in proportion to the light and heat which they receive, being paler in a more diffused light than when they are exposed to the more direct solar rays. During the prevalence of light, the leaves of plants absorb carbonic acid, and part with oxygen, and thus purify the atmosphere for the use of man and animals, and this process again, goes on just in proportion to the intensity of the sun's rays to which the leaves are exposed. The decomposition of earbonie acid, and the acquisi tion of carbon in a solid state, by the plant, is hastened or retarded in proportion to the amount of light received. So also the intensity of color and quantity of secretions are in proportion to their exposure to the light and air, as is shown by the deeper color of the upper portion of the leaves of plants. This is further proved by the fact that plants grown in a medium from which light is excluded, form neither color nor secre tions—as in the blanching of celery, previously noticed. As plants derive an essential portion of their food from the air by the action of light, therefore those greenhouses and conservatories that admit most light are best adapted to the forcing and cultivation of plants. It has been found by experiment that light passes more freely through a curvilinear than through a plain roof, and through glass forming an acute angle with the horizon than through glass placed per pendicularly. Consequently aplane roof, with perpendicular glass sides, is tht worst possible form for greenhouse purposes. As light passes more freely through clear, thin, colored glass, the former should only be used. Poisonous gases, in very minute quantity, act with great energy upon vegetation. A ten thousandth part of sulphuric acid gas is quickly fatal to the health of plants. Hence the sickly appearance of many forms of vegetation, especially ever greens in cities. The trouble with gases from the old-fashioned flue, has pretty generally led to their abolition in greenhouses, and to the introduction, instead, of heating by means of hot water. The process has now become so sim plified, and so easily worked, that a man who should put up a permanent greenhouse or a conservatory to be heated by the old-fashioned flue, would be laughed at by practical men. They are only admissible, at best, in temporary structures. It is only within a comparatively few years that scientific men have given their attention to the practical investigation of the phenomena connected with agriculture. The conclusions of mere book theorists have done much to retard the progress of real agricultural science. Governments have waked up to the importance of scientific agricultural investiga tions. When the mere theorizing stage shall have passed away with us, as it is passing away in Germany and some other European countries, then and not till then shall we begin to make true progress in the right direction.