The colours of organic bodies in general may be considered as a higher kind of chemical operation, for which reason the ancients employed the word concoction, πέψις, to designate the process. All the elementary colours, as well as the combined and secondary hues, appear on the surface of organic productions, while on the other hand, the interior, if not colourless, appears, strictly speaking, negative when brought to the light. As we propose to communicate our views respecting organic nature, to a certain extent, in another place, we only insert here what has been before connected with the doctrine of colours, while it may serve as an introduction to the further consideration of the views alluded to: and first, of plants. 618. Seeds, bulbs, roots, and what is generally shut out from the light, or immediately surrounded by the earth, appear, for the most part, white. 619. Plants reared from seed, in darkness, are white, or approaching to yellow. Light, on the other hand, in acting on their colours, acts at the same time on their form. 620. Plants which grow in darkness make, it is true, long shoots from joint to joint: but the stems between two joints are thus longer than they should be; no side stems are produced, and the metamorphosis of the plant does not take place. 621. Light, on the other hand, places it at once in an active state; the plant appears green, and the course of the metamorphosis proceeds uninterruptedly to the period of reproduction. 622. We know that the leaves of the stem are only preparations and pre-significations of the instruments of florification and fructification, and accordingly we can already see colours in the leaves of the stem which, as it were, announce the flower from afar, as is the case in the amaranthus. 623. There are white flowers whose petals have wrought or refined themselves to the greatest purity; there are coloured ones, in which the elementary hues may be said to fluctuate to and fro. There are some which, in tending to the higher state, have only partially emancipated themselves from the green of the plant. 624. Flowers of the same genus, and even of the same kind, are found of all colours. Roses, and particularly mallows, for example, vary through a great portion of the colorific circle from white to yellow, then through red-yellow to bright red, and from thence to the darkest hue it can exhibit as it approaches blue. 625. Others already begin from a higher degree in the scale, as, for example, the poppy, which is yellow-red in the first instance, and which afterwards approaches a violet hue. 626. Yet the same colours in species, varieties, and even in families and classes, if not constant, are still predominant, especially the yellow colour: blue is throughout rarer. 627.