Where the petals are united the same law holds good. In regular flowers, like the lilies, the colouration is equal. In irregular flowers, like the snapdragon and foxglove, the decoration is irregular. In Gloxinia the petals may be either regular or irregular, and the decoration changes in concert. A very instructive case was noticed by one of us in _Lamium galeobdolon_, or yellow Archangel. This plant is normally a labiate with the usual irregular corolla, but we have found it regular, and in this instance the normal irregular decoration was changed to a regular pattern on each petal. In gamopetalous flowers the line of junction of the petals is frequently marked with colour, and we know of no case in which a pattern runs deliberately across this structure line, though a blotch may spread from it. When we remember that flowers are absolutely the result of the efforts of plants to secure the fertilizing attention of insects, and that they are supreme efforts, put forth at the expense of a great deal of vegetable energy--that they are sacrifices to the necessity for offspring--it does strike us forcibly when we see that even under these circumstances the great law of structural decoration has to be adhered to. [Illustration: Plate XII. FLOWERS.] CHAPTER XVI. CONCLUSIONS. We have now, more or less fully, examined into the system of colouration in the living world, and have drawn certain inferences from the facts observed. It appears that colouration began--perhaps as a product of digestion--by the application of pigment to the organs of transparent creatures. Supposing that evolution be true--and, if we may not accept this theory there is no use in induction whatever--it must follow that even the highest animals have in the past been transparent objects. This was admirably illustrated by Prof. Ray Lankester in a lecture on the development of the eyes of certain animals, before the British Association meeting at Sheffield, in which it was shown that the eyes commenced below the surface, and were useful even then, for its "body was full of light." Granting this, it follows that the fundamental law of decoration is a structural one. Assuming, as we do, that memory has played a most important part in evolution, it follows that all living matter has a profound experience in decorating its organs--it is knowledge just as anciently acquired, and as perfectly, as the power of digestion. This colour was produced under the influence of light--so it is even in opaque animals. With a knowledge so far reaching, we might expect that even in opaque animals the colouring would still follow structural lines, and there should still be traces of this, more or less distinct.