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strange phenomena can be observed in the transition state 
of negative phototaxis to insensibility as regards light. 
$ 5. The Phototaxis of Chlamydomonas. 
Of late there appeared a publication of Buder (1917), 
in which there is said a good deal of Chlamydomonas 
variabilis. The data, which can be found there about the 
phototactical movements of this Alga, coincide absolutely 
with what I observed ofit. In distilled water and solutions 
in which there is not too much acid, base or salt Chlamy- 
domonas reacts negatively to the light. Buder observed 
that the Alga did not always react with the same certainty. 
For the case, in which the reaction did not run very 
smooth, he used the term “Streuung'. 
J have found that “Streuung” takes place when acid, 
base or salt is added to the water. This goes so far, that 
the sensibility to light absolutely disappears. Just as with 
the geotaxis this is accompanied by a strongly diminished 
motility. The concentration necessary to cause, that the 
object no longer reacts to the light, well nigh corresponds 
to the concentration, that annuls the geotaxis. Besides the 
fact that the Alga reacts negatively phototactically the 
object can also be positively phototactical. [| am unable 
to call up this situation arbitrarily. However Î can assure, 
that the positive phototaxis only occurs in the transition- 
case of negatively phototactical to unsusceptible to light. 
In the cultures we very often meet with this state of 
things and sometimes some days at a stretch in the same 
culture. Before that time the organisms react negatively 
to the light after that they can become unsensible to 
light. It is a matter of fact that want of oxygen is not 
able to bring about the positive phototaxis. 
