The colour which is found superficially in the flower and penetratingly in the fruit, spreads itself through all the remaining parts, colouring the roots and the juices of the stem, and this with a very rich and powerful hue.
So, again, the colour of the wood passes from yellow through the different degrees of red up to pure red and on to brown. Blue woods are unknown to me; and thus in this degree of organisation the active side exhibits itself powerfully, although both principles appear balanced in the general green of the plant.
We have seen above that the germ pushing from the earth is generally white and yellowish, but that by means of the action of light and air it acquires a green colour. The same happens with young leaves of trees, as may be seen, for example, in the birch, the young leaves of which are yellowish, and if boiled, yield a beautiful yellow juice: afterwards they become greener, while the leaves of other trees become gradually blue-green.
Thus a yellow ingredient appears to belong more essentially to leaves than a blue one; for this last vanishes in the autumn, and the yellow of the leaf appears changed to a brown colour. Still more remarkable, however, are the particular cases where leaves in autumn again become pure yellow, and others increase to the brightest red.
Other plants, again, may, by artificial treatment be entirely converted to a colouring matter, which is as fine, active, and infinitely divisible as any other. Indigo and madder, with which so much is effected, are examples: lichens are also used for dyes.