266 
ORIGIN OF ORGANIC COLOUR. 
be absorbed, and these are reflected as green light; in the blossom 
a still further molecular change confines the absorption to some one 
portion of the spectrum, not always the same portion, and the 
remainder is reflected as one of the brilliant secondary hues. 
In this gradation the leading feature appears to be a successive 
simplification of molecular motion. In the first case, the molecules 
are able to move freely in all directions ; in the second case, their 
motions are limited to short vibrations and long ones; in the 
third, the molecular motions have all become nearly similar, some¬ 
times they have all become capable of short vibrations only, some¬ 
times of long ones only, and sometimes of those of intermediate 
length only, but in each instance the simplification and unification 
of the molecular condition is shown by the brilliancy of the 
compound light which is reflected. 
What is the precise nature of the molecular changes thus 
indicated I am not able to prove ; but some clue to it may be found 
in the following suggestions :— 
The assimilation of food is a phenomenon peculiar to organic 
life. All organisms absorb food, appropriate a large part of the 
energy of the food material, and reject the exhausted refuse. 
During the whole of life some of this energy is expended in the 
various activities of the living body ; during the earlier portion of 
life some of it is also expended in the phenomenon of growth ; while 
a certain balance remains unexpended in any visible action and 
becomes concentrated within the organism, giving to the matured 
creature a greater reserve of energy than existed in the young 
form. 
This concentrated energy must almost certainly exist within 
the organism in the form of increased molecular motion. The 
molecules of all bodies whose temperature is above the absolute 
zero are supposed to be in constant vibration, such vibrations 
producing wave motions which are communicated to the surround¬ 
ing ether as heat-waves. Any increase of energy will enhance the 
molecular vibrations, either in velocity, or amplitude, or both. If 
the amplitude only is enhanced, the wave-lengths will be increased ; 
December, 1893. 
