Chromatic Adaptation. 241 
final colour, and so the culture goes on gradually improving its 
biological position. 
It is interesting to note that if the cultures were brought back 
to white diffuse light they retained for months the colour that they 
had acquired behind the coloured screen, and even the new cells 
formed thus under natural illumination exhibited the acquired 
colour. The ultimate fate of these nascent new “ forms ” has not 
yet been announced. 
As has been pointed out, white daylight probably supplies sufficient 
of all the spectral radiations to allow any of the OsciUaria-colours 
to assimilate abundantly, so that there would be no assimilatory 
gain in the new forms reverting to their ancestral colour. 
Gaidukov’s first paper gives very excellent full details of the 
colour-changes and is illustrated with coloured figures of the 
filaments themselves, of the colour-screens and of the absorption 
spectra of the different coloured pigments. Also there are given 
detailed measurements of the change of absorption for different 
rays as one pigment passes into another. The author draws 
attention to the fact that each stage of colour-progression passes by 
imperceptible gradations into the next and that here, as elsewhere, 
Natura non facit saltum. 
The different shades of colour are due to modifications, not of 
the chlorophyll in the chromatophore, but of the water-soluble 
proteid pigment which is here called the adaptational pigment. 
If abundant this completely masks the green colour. 
It has generally been held that the blue water-soluble pigment 
of the Cyanophyceae belongs to the same class as the red and 
brown pigments of the Rhodophyceae and Phaeophyceae but it 
would appear now that when the blue-green Oscillaria becomes red 
under the influence of green light it developes a pigment identical 
with that of the Rhodophyceae. 
The characteristic secondary proteid pigments of these three 
groups of algae can be crystallised from their watery solutions so 
that in time we may hope to know their chemical relation. The 
watery solutions are slowly decomposed by light but show no 
indication of complementary colour change outside the living cell. 
It is interesting to note that the pure green algae and the 
higher plants which have evolved from them, appear to have no 
water-soluble proteid pigment in their chromatophore though to 
the best of the writer’s knowledge such a pigment has never been 
carefully looked for. If so, they would seem to be devoid of, or to 
have lost, the material basis for carrying out complementary 
