Green, which occupies the middle station in the natural scale of colours and in relation to light and shade, is the second of the secondary colours. It is composed of the extreme primaries, _yellow_ and _blue_, and is most perfect in hue when constituted in the proportions of three of yellow to eight of blue of equal intensities; because such a green will exactly neutralize and contrast a perfect red in the ratio of eleven to five, either of space or power. Of all compound colours, green is the most effective, distinct, and striking, causing surprise and delight when first produced by a mixture of blue and yellow, so dissimilar to its constituents does it appear to the untutored eye. Compounded with orange, green converts it into the one extreme tertiary _citrine_; while mixed with purple, it becomes the other extreme tertiary _olive_: hence its relations and accordances are more general, and its contrasts more agreeable with all colours, than those of any other individual colour. Accordingly it has been adopted very wisely in nature as the common garb of the vegetal creation. It is, indeed, in every respect a central or medial colour, being the contrast, compensatory in the proportion of eleven to five, of the middle primary _red_, on the one hand, and of the middle tertiary _russet_, on the other; while, unlike the other secondaries, all its hues, whether tending to blue or yellow, are of the same denomination. These attributes of green, which render it so universally effective in contrasting colours, cause it also to become the least useful in compounding them, and the most apt to defile other colours in mixture. Nevertheless it forms valuable semi-neutrals of the olive class with _black_, for of such subdued tones are those greens by which the more vivid tints of nature are opposed. Accordingly, the various greens of foliage are always more or less semi-neutral in hue. As green is the most general colour of vegetal nature and principal in foliage; so red, its harmonizing colour, with compounds of red, is most general and principal in flowers. Purple flowers are commonly contrasted with centres or variegations of bright yellow, as blue flowers are with like relievings of orange; and there is a prevailing hue, or character, in the green colour of the foliage of almost every plant, by which it is harmonized with the colours of its flowers.