342 Hoyt: CULTURES OF SPIROGYRA 
transfer was killed in about two days, and the material which then 
replaced it lived fifteen days, but was in apparently poor condition 
at the end of that time and was replaced. The material of this 
fifth transfer preserved an apparently healthy condition for forty- 
four days, at which time the experiment was discontinued. The 
toxic water had been réndered nontoxic simply by treatment with 
alga filaments. A clearer example of the effects of plants in re- 
moving or counteracting the toxic substances of a solution would 
be difficult to imagine. Similar results were obtained by Dandeno 
(7) upon growing corn seedlings in toxic solutions of HCl and 
H.SO,. 
Toxic water may be greatly improved for Spirogyra by previous 
treatment with another alga. A mass of Ulothrix (with a few 
Spirogyra filaments) was allowed to remain twenty-eight days in 
ordinary distilled water (III, 35), while a control of a similar dish 
with another sample of the same water, but without alga, stood 
beside the first. At the end of this period the Ulothrix was re- 
moved and Spirogyra from the stock culture was transferred to 
each of the two dishes. In the water which had been previously 
treated with Ulothrix the Spirogyra lived, albeit in rather poor 
condition, for twenty-two days, while in the untreated water of 
the control all filaments were killed within eighteen hours. 
In connection with the above observations on the effectiveness 
of alga filaments in correcting the toxicity of ordinary distilled 
water, it should be noted that, in all these experiments, the amount 
of Spirogyra added, in proportion to the amount of medium 
employed, exerted a considerable influence upon the results. A 
large amount of the alga was able to live in a small amount of a 
decidedly toxic medium. In all such cases the filaments on the 
outside of the mass were killed while those within remained in 
good condition. Similar results have been obtained by Nageli 
(20), Deherain and Demoussy (8), Bullot (6), Dandeno (7), and 
Bokorny (3). In the same connection, water from the stock 
culture of Spirogyra, tested by the method used in these experi- 
ments, allowed a good growth (III, 36), but seemed less favorable 
than the water from a vigorous culture of Nitella (III, 37). 
Although some of the experiments which have been considered 
were not repeated as many times as might be desirable, the different 
