Primary colors are three: red, yellow, and blue.
Red is the color of greatest heat.
Yellow is the color of greatest light.
Blue is the color of chemical change.
In accordance with this philosophical truth, we should naturally expect to find a preponderance of blue rays from the sun in the spring time, and so it is.
These rays preponderate at the time of ploughing, sowing, and germination.
In the summer time, after the plant has started from the ground, and requires vigorous leaves to bring it to perfection ere the cold winter rolls around once more, we have the yellow rays. 'Light, more light,' is then the cry of nature, and as not even length of days affords this element in sufficient completeness, the sun darts his brightest beams in 'the leafy month of June.'
Later still in the year, after germination is past and growth perfected, comes the necessity of heat rays to ripen fruit, vegetables, and grain, and nature's behests are obeyed in the then preponderance of the red rays. Much of this effect may be due to the media through which the sun's rays pass. A sensitized photographic paper is not colored as much at an altitude of three miles in half an hour as is a similar paper upon the earth's surface in one moment. At any season of the year, gardeners can either stimulate or retard germination as they place a blue or yellow glass over the nursling. That the growth of plants is not due alone to the rays of the sun we can, without experiment, convince ourselves, as even ordinary observers are well aware that upon some days plants shoot up so rapidly as to grow almost visibly under their eyes, and in other conditions of the atmosphere seemingly remain dormant for days.
The germinating influence, let it be due either to peculiar rays alone, or to atmospheric state, does not contain much coloring matter. The first spring flowers are of a pale color; as summer advances we have brighter hues, but not until the approach of fall do we see Flora in all her gorgeousness of coloring. The paleness of mountain and arctic flowers, and the brilliancy of those of the tropics, point to the same cause which gives the temperate zones their brightest flowers when heat rays preponderate.
As depth of color seems connected with the red or heat rays; so perfume belongs rightfully to the summer blossoms; when light is the strongest, then we have our pinks, and roses, and lilies.