240 
F. F. Blackman. 
investigated by Gaidukov 1 in which “complementary chromatic 
adaptation” can be brought about in the course of a few weeks, and 
all the details of the change have been followed by him. 
He found that filaments of Oscillaria possess the power of 
changing their colour when grown behind coloured glass or coloured 
solutions and always in the direction of taking on the complementary 
colour to the light which they are made to exist in, and so absorbing 
it more efficiently. According to the views here put forward, 
this would be a distinct biological gain only if the light were 
so weakened that it became the limiting factor in assimilation. In 
this connection it is significant to note that Gaidukov’s cultures 
were grown inside the laboratory, though within a yard of a big 
south window, and the colour screens used were mostly deeply 
coloured. 
Oscillaria sancta, which is violet in white diffuse daylight, was 
first investigated, and pure cultures growing on earth or agar in 
Petri dishes, were kept in the different coloured lights. After one 
to four weeks they were found to have taken on the complementary 
colour, being greenish in red light, blue-green in yellow brown light, 
and yellow-brown in blue light. During this time the cultures had 
grown rapidly, so that the final colour w r as due chiefly to newly-formed 
cells. Another species, O.caldariorum, which is blue-green in daylight, 
gave quite similar colour-changes. 
When a filament is transferred from one light to another which 
is spectrally remote from it, as from red to blue, it does not at once 
begin to assume its correct final reddish colour, but passes in 
succession through a long series of intermediate stages of coloura¬ 
tion, being the colours approximately complementary to the 
intermediate spectral lights in order. This series of colours is 
given by Gaidukov as (1) sky-blue, (2) blue-green, (3) verdigris-green, 
(4) grey-green, (5) whitish-grey, (6) violet to brown-violet, (7) brown 
(8) orange to reddish. 0. sancta in ordinary white light happens 
to have colouration 6. Transferred to red light it passes up the 
series to 1. Placed in blue light it passes through 7 to colour 8. 
O. caldariorum happens in white light to have colour 2 and 
transferred to green light it passes down the series to 7 or 8. 
As the individual cells are multiplying all the time it may be 
that each generation only takes a short step in the direction of the 
1 Gaidukov. Uber den Einfluss farbigen Lichts auf dieFarbung 
lebender Oscillarien. 
(a) . Anhang zu Abh. k. Prenss. Akad. Wiss. Berlin, 1902, v. 
( b ) . Ber. deut. bot. Gesell., Bd. xxi., Oct., 1903. 
(r). ,, ,, ,, Nov., 1903. 
