When we come to flowers, the same general law prevails, and is generally more marked in wild than in cultivated forms, which have been much, and to some extent unnaturally, modified. Broadly speaking, when a flower is regular the decoration is alike on all the parts; the petals are alike in size, the decoration is similar in each, but where they differ in size the decoration changes. Thus, in Pelargoniums we may find all five petals alike, or the two upper petals may be longer or shorter than the lower three. In the first case each is coloured similarly, in the other the colour pattern varies with the size of the petal. The same may be seen in Rhododendron.
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.
Plate XII.
FLOWERS.