Hoyt: CULTURES OF SPIROGYRA 347 
the bases: calcium, barium, magnesium, strontium, cobalt, 
aluminium, lead, zinc, and chromium. 
The experimentation about to be reported, upon the relation to 
Spirogyra of the salt content of the medium, is merely qualitative, 
the aim being to gain some knowledge of a number of possible 
conditions in algal-cultures rather than to investigate any of the 
chemical questions here encountered. No attention has been 
| given to the chemical characteristics of the salts employed, the 
solutions having been prepared on the percentage basis, and the 
terminology of percentage will be retained in the discussions. 
The experiments are partly repetitions of those of Benecke (r). 
Aside from the effect of dissolved salts to counteract the toxicity 
of salt solutions, these experiments also include a number of tests 
bearing upon the influence of undissolved materials upon this 
same sort of toxicity. 
Throughout these experiments no water was used which had 
not been shown to be nontoxic; it had all been distilled from 
animal charcoal in glass, condensed in glass, and collected in glass. 
Precautions were always taken to avoid possible contamination of 
the dishes used, especially in the case of the cultures without 
calcium. All salts used, except the CaCOs, were those of Merck. 
The experiments are listed, with their results, in TABLE V. 
For the study of the influence of calcium in the medium a cal- 
cium-free solution was prepared from equal portions by weight of 
KNO;, K,HPO,, KCI, and MgSO;. . This solution was tested in two 
concentrations, 0.4 and 0.1 per cent (of total salt content by 
weight), and both proved highly injurious to the Spirogyra here 
employed (V, 1). The addition of calcium-free animal charcoal 
produced no improvement in either case (V, 2), but common wood 
charcoal, pulverized, which was shown by test to contain some 
calcium, improved the weaker solution (V, 3). In the weaker 
solution a small amount of CaCl produced about as marked 
improvement as did wood charcoal (V, 4), a trace of CaCO; 
allowed still better growth (V, 5), while an abundance of the last- 
named, only slightly soluble salt kept the alga in excellent condi- 
tion during the entire period of the experiment—35 days (V, 5). 
These same experiments, performed with solutions prepared from 
ordinary distilled water, gave the same results, except that the 
