96 Colouration in Animals and Plants. 



in the Calatheas we have dark marks running along the veins. In 

 Draccena ferrea we have a dark green leaf, with a red border and tip, 

 the red running downwards along the veins. This action may be 

 continued until the leaf is all red except the mid-rib, which remains 

 green. In long net-veined leaves we may cite Pavetta Borbonica, 

 whose dark green blade has a crimson mid-rib. Of unsymmetrical 

 leaves those in the plate may suffice. 



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 Pelar- 

 goniums 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. 



