Hoyt: CULTURES OF SPIROGYRA 345 
by agar jelly appears also to have been due to adsorptive action, 
though a discussion of this matter will not be given place here. 
It is interesting to remark that addition of sand, cotton, and filter 
paper failed to produce any correction of the ordinary distilled 
water of these experiments, although these substances have been 
found by Nageli (20), Dandeno (7), True and Oglevee (36) and 
Jensen (9), to be active in improving other toxic solutions. The 
difference thus noted may be of course due either to a difference 
in the toxic substances dealt with or to differences in the solids 
used. Breazeale (5) obtained similar negative results upon adding 
quartz flour, filter paper, paraffin, or sand to solutions of H:SO, 
which were toxic to corn seedlings. He suggested that the failure 
of these substances to reduce the toxicity of the solutions was 
due to the high concentration of HzSO, necessary to produce toxic 
action, and the consequent relatively slight adsorption of the acid 
by the solids. This explanation can not, however, apply to 
the results described above, since in these experiments the amounts 
of the toxic substances were extremely small. 
In considering the behavior of Spirogyra in different nutrient 
media (see p. 335), it has been observed that the optimum con- 
centration of the solution appeared to be a function of the kind of 
water used. With solutions that contained salts in the propor- 
tions adopted by Molisch and Crone and were prepared with non- 
toxic water, the optimum concentration for the growth of Spirogrya 
was found to be from 0.05 to 0.1 per cent, while similar solutions 
prepared with ordinary distilled water exhibited an optimum con- 
centration ten times as great. It thus appears that the toxicity 
of the ordinary distilled water was more or less overcome by the 
larger amount of nutrient salts present and that, conversely, the 
retarding effect of relatively high salt concentration was counter- 
balanced by the presence of the toxic material of the water. 
The influence of dissolved salts in overcoming the toxicity of 
solutions has been noted by other authors,* but the whole question 
here raised is not at present in a state to warrant an attempt at 
detailed discussion. It is obviously related to the general problem 
of physiological antagonism. Some points on salt antagonism 
will be brought forward in the succeeding section. es ad 
* Breazeale (4), Livingston ef al. (11), Livingston (12), Sumner (35), Schreiner 
and Reed (28), and Schreiner and Skinner (32, 33)- 
