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in the dark. There is always a part of the organisms that 
does not mount in the vertical tube. These individuals 
hardly more. With Massart the experiment generally 
takes an hour. 
We also find something of geotaxis of Chlamydomonas 
pulvisculus with P. Jansen (1893, page 428). He, too, 
finds that the object is negative geotactical; that we have 
to do the experiments in a tube, no longer than about 
four centimeters and that often individuals are found, 
which sink down to the bottom, apparently passive. 
From all this we see, that the individuals of Chlamy- 
domonas pulvisculus did not react so very nicely in the 
state, in which the examiners quoted, use them. 
With Chlamydomonas variabilis Dangeard Ï noticed a 
very distinct motion towards the bottom of the vessel. 
Within ten minutes all the organisms had reached the 
bottom. In the dark the phenomenon, as a rule, took 
place in the same way. In some cases the experiment 
did not succeed in the dark. Whether this was a con- 
sequence of the sudden change light-dark, Î cannot 
judge. It is not so easy to find out that here we have to 
do with positive geotaxis; as the Algae react at the same 
time negatively phototactically. In bright light we get by 
the two movements, when we put the algae into distilled 
water, into a thin glass tube placed vertically, a dense 
green stripe on the shadow-side, which sinks to the bottom 
comparatively fast (see fig. 1 B. and C). With a weak 
objective we can follow the motion of the algae with a 
microscope. Then it seems that Chlamydomonas moves 
downwards absolutely passive, that means we see the 
organisms swim forwards, backwards, downwards and 
upwards. When working in very weak white light or in 
red light, we perceive, that the general direction of the 
movements is downwards. Ï speak of a positive geotaxis, 
but will only say, that Chlamydomonas variabilis moves 
