CHAPTERAIN 
Contemplations and conclusions, to which the 
experiments give rise. 
$ 1. The conduct of Chlamydomonas in solutions with 
a slight, constant salt concentration and a 
gradually increasing H-ion concentration. 
In the first place I have pointed out as well as possible, 
that the faillure of the reaction to gravity can be caused 
by a change of the amount of hydrions or of hydroxylions. 
To this purpose a series of solutions was made, which 
contain all 0,01 normal sodium acetate and changing 
quantities of free acetic acid or free sodium hydroxyde. 
In these solutions we can cause the H-ion concentration 
to change regularly, while the number of the other ions 
remains well-nigh the same. The not dissociated molecules 
of acetic acid are not always present in the same number. 
We must here rely on experience, which teaches, that 
such small quantities of not dissociated molecules have no 
important influence. 
If we put the algae in these solutions we find, that 
they do not show the reaction to gravity in those numbers 
of the series, which are most acid, neither in those solutions, 
which are most alkaline. It is a matter of course, that it 
cannot be said beforehand, whether a series of solutions 
which one has made, contains such solutions the first time 
