Hoyt: CULTURES OF SPIROGYRA 349 
ing solid CaCO 3, however, the alga remained in good condition 
for seven days and had many filaments apparently uninjured at 
the end of fifteen days, when the experiment was discontinued 
(V, 17). These and other lines of evidence obtained during the 
progress of this work seem to indicate that the beneficial effect of 
the powdered CaCO; was due in part to other causes than the 
mere addition of calcium to the solution, probably to its adsorptive 
action. This suggestion is further supported by the results of 
Livingston et al. (rr) Snyder and Cook (34), Breazeale (5), and 
Schreiner and Reed (28). 
The colloidal solution of platinum already referred to rendered 
a 0.01 per cent solution of MgSO, decidedly less toxic (V, 18), but 
the addition of 0.008 per cent PtCl, to a 0.01 per cent MgSO, 
solution produced no observable improvement. 
Although, as was noted above, the addition of 0.1 per cent 
of KCl rendered a 0.1 per cent solution of MgSO, less toxic, a 
0.1 per cent solution of KCI alone was decidedly more toxic than 
this mixture (V, 20), and a 0.4 per cent solution of KCI was fatal 
within two days (V, 19). This result is in agreement with the work 
of Osterhout (22). The colloidal solution of platinum produced 
improvement in a 0.1 per cent solution of KCI (V, 21). Addition 
of 0.1 per cent of CaCl: to a 0.1 per cent solution of KCI rendered 
the latter slightly less toxic (V, 22), although a 0.2 per cent solu- 
tion of CaCl was fatal within a few hours or days (V, 23). 
Two experiments were made bearing upon the relative endur- 
ance, in solutions of the above salts, of samples of Spirogyra 
originally from the same source, but subjected for a time to dif- 
ferent surroundings. One portion of an alga culture which had 
been growing vigorously for sixty-six days in 0.1 per cent Crone’s 
solution was rinsed in nontoxic water and placed in a solution 
containing 0.1 per cent of KCI and 0.1 per cent of CaCh (V, 24) 
and another portion of the same culture was likewise rinsed and 
placed inao.2 per cent solution of CaCk (V, 25). On the following 
day were added to both of these cultures samples of Spirogyra 
from the stock jar. In both cases the solution was injurious to 
both samples of the alga, but decidedly less so to the filaments from 
Crone’s solution than to those from the stock culture (V, 22, 23). 
This result again emphasizes the well-known fact, already men- 
