176 THE COLOURS OF FLOWERS. 
colours which surround us in the vegetable world. The type of a perfect 
and complete vegetable is a flowering tree or shrub, such as a hawthorn, 
an apple, or a laburnum. In plants of this kind we have all the 
great systems of vegetable structure fully developed—the stem, the 
foliage, and the blossom. In herbaceous plants aud all monocotyledons 
the stem system is imperfect; in cactuses and some euphorbias the 
foliage is never developed; in grasses, conifers, and many forest trees 
the flower system is defective; but in a true flowering tree you have 
everything complete. Look then at an apple tree or a laburnum; the 
prevailing colours in the stem and branches are brown, grey, or olive: in 
the foliage, green; in the blossom, white, pink} and yellow. And this 
relation of colour to each system of structure will bé found throughout 
the vegetable world with few exceptions—dark feeble colours in the stem 
system, the primary green in the foliage, and the brilliant secondaries 
in perfected blossom. Now look a little deeper and see why this should 
be so. Stems are grey or brown because they absorb nearly all of the 
three component colours of white light, and in nearly equal proportion, 
reflecting a little of each. Leaves are green because they absorb two of 
the component colours, and reflect nearly the whole of the other! 
Flowers are yellow, blue, or pink because they absorb only one of the 
component colours, reflecting the other two. Hére, then, is a regular 
gradation from the stem, through the foliage, to the flower. First three 
colours are absorbed, then two, and, lastly, one. How is this to be 
accounted for? It is not pretended that insects have anything to 
do with differentiating the foliage from the stem: Why should 
their jinterferencd be thought nécessary in differentiating the 
flower from the foliage, which is a precisely analogous process? 
Ié is surely a process dependent upon the fundamental laws of organic 
growth: I think an explanation may be found, but it is, perhaps, tog 
abstruse to be more than hinted at in this address. The absorption of 
light waves depends upon the molecular structure of the material on 
which it falls) Where such material contains molecules capable of 
vibrations of all lengths mixed up together, all the light waves will bé 
absorbed. This is probably the condition of vegetable stems. Whén the 
molecules are so far sorted out and reduced to order that they will only 
vibrate in two modes, two only of the primary colours are absorbed, and 
the other reflected. This is the condition of leaves. When actual 
uniformity of molecular conditions is attained only one colour can be 
absorbed, the other two must be reflected, and the object appears brilliant 
with one or other of the showy secondary colours. This is the condition 
of flowers. I believe it can be shown that the reducing to order, and, 
finally, to uniformity of & group of very diverse moleculés is one of the 
essential conditions of organic life; that the gradual development of 
colour is a necessary result of this A Sst law; that, therefore, coloured 
flowers were to be expected at a certain epoch in the development of this 
world, and that their number and brilliancy will still increase as the ages 
roll forward. Insects may help the process, but the great flood of 
organic life would not be stopped in its career though every bee and 
butterfly should perish: 
