334 Hoyt: CULTURES OF SPIROGYRA 
one; results obtained with material brought from various other 
conditions to the laboratory cannot be interpreted as caused by 
changes in the nature of the culture solution alone, a point well 
emphasized by some of the considerations to be brought out below. 
The method here followed was to transfer a few (about 30 to 
50) filaments from the stock culture to about ten cubic centimeters 
of the medium to be tested, in a covered glass dish. These trans- 
fers were made late in the afternoon, and the cultures were sub- 
jected to microscopic examination, without removal from the 
culture dishes, on the next morning and on succeeding days until 
final results were obtained. The experiments lasted for periods 
of from one to eighty-six days. The condition of each culture 
was recorded in the following terms. Excellent means that, at 
most, only a few cells showed injury; good, that considerably 
more than half of the filaments seemed uninjured; poor, that more 
than half were injured; dead, that practically every cell was dead. 
The tables used in this paper have been constructed from the 
daily records by stating in similar terms the general condition of 
the cultures throughout the experiments. 
Precautions were of course taken to have the dishes and instru- 
ments as clean as possible. Any dish once used for a poisonous 
solution was discarded at the end of that experiment, and dishes 
were sometimes interchanged and furnished with fresh supplies 
of the media to be tested. The different lots of special distilled 
water did not enter into experiments until they had been found 
to be harmless to the plant here used. In most cases about the 
same amounts of media were used in the different experiments; 
the quantity. of solution as related to the number of cells in any 
culture is to be considered as an important factor in all experiments 
bearing upon the relation of the nature of the medium to the 
behavior of organisms existing therein. 
I. NUTRIENT SOLUTIONS 
The nutrient media used were all prepared according to the 
formulae given by Kiister (10), being those of Sachs, Knop,; 
Molisch, and Crone.* These were afterward diluted to the — 
* These solutions contained salts in the following proportions: 
