22 
speedily is superseded by light, the dark-growth-response cannot fully 
develop: the retardation of growth is earlier changed into increase 
of growth, so that the minimum is slighter (77'/,—$5'/, °/, instead 
of 70—75°/,) and consequently seems to be a little earlier (after 
7—9 min. instead of 8—12 min.). The beginning and the maximum 
of the light-growth-response on the contrary show themselves later 
with longer darkening, demonstrating in that way that it is the 
response to the return of light. The maximum was found with 1, 
2, 3, 5, 7'/,, 12°/,, 20 minutes of darkening, resp. at 10'/,—183, 
8—10; 8 10,00 a ls 9 | Ola Ola Ome eee 
after the return of light, while this maximum with complete adap- 
tation to the dark (see Licht u. Wachstum III p. 102) has also 
been found at 7—8'/, minutes after the beginning of 64 M.C. This 
latter reaction has been added for comparison as 9*" curve to fig. 1. 
This shows that the first maximum, even the successive sinking 
and a second maximum observed at one time (1918) in permanent 
64 M.C., now 1920 showed itself again after a darkening of only 
20 minutes. The successive curves demonstrate, how by taking the 
dark periods longer and longer, we are able to analyse the response 
to a short darkening in a dark-growth-response (A) result of dark- 
fall, and a light-growth-response (b—C—D), result of subsequent 
exposure to light. 
Meanwhile Sierp (1921) has considered with Avena the response 
of growth in short periods of dark. In this summary we can but 
refer to this. Though the transition from dark to light (64 M.C.) in 
the successive experiments is in a physical sense every time equally 
great, this transition causes an ever greater maximum in the growth 
(resp. 103'/,—112—118—124—126—145 and 163°/,), according as 
the cell has been darkened longer. By this it is already shown, 
that the cell adapted to 64 M.C. has greatly lost its sensitiveness 
and that the sensitiveness after the darkening increases very rapidly 
already from the first minutes. This dark-adaptation (= disappear- 
ance of light adaptation) is further shown by the following expe- 
riments. 
V. The adaptation to the dark of a cell used to light may be 
demonstrated in two ways: A. by applying an equal quantity of 
light at different times after the darkening and considering how 
the response to this light-stimulus increases according as the cell has 
been longer in the dark; B. by determining how great the threshold 
of stimulation is at different points of time after the darkening. 
Experiment A*: A quantity of 256 M.C.S. (in 4sec.) applied was 
