ON THE ORIGIN OF ORGANIC COLOUR.* 
BY F. T. MOTT, F.R.G.S. 
In studying the colours exhibited by plants it must have been 
very frequently noticed that in nearly every complete plant of the 
higher orders there are three distinct schemes of colour, viz. :—The 
dull browns, olives, and maroons of the stems and branches ; the 
varied greens of the foliage; and the brilliant reds, yellows, and 
blues of the blossom. 
Since each of these three colour-schemes is almost universally 
associated with one particular group of organs, there is the highest 
probability that some permanent and fundamental relation exists 
between the organ and its colour. 
Colour is supposed to depend upon the amount of absorption to 
which the white light is subjected within the tissues upon which it 
falls. The three colour-schemes of plants are directly related to 
each other in the amount of such absorption which they imply. 
The dark colours of the stems and branches indicate an almost 
total absorption of the light waves of every length ; the greens of 
the foliage indicate a great decrease of absorption of the waves of 
medium length ; while the brilliant hues of the flowers show that 
absorption has been reduced to a minimum. 
Why should there be this gradation in the absorbing capacity 
from the stem, through the foliage to the flower? It is true that 
the stem and branches are the least vitalised parts ; that in the 
foliage the active functions of life are much more energetically 
developed; and that in the flower there is a still greater concentra¬ 
tion of active energy. But how is this gradation of vitality 
correlated with the gradation of absorption ? 
In the bark of the stem and branches the molecular structure 
is such that light waves of all lengths are able to be taken up and 
assimilated ; in the foliage some change in the molecular structure 
has taken place, so that the waves of medium length can no longer 
* Read in Section D of the British Association, at Nottingham, September 
15th,1893. 
December, 1893. 
