504 



THE AMERICAN NATURALIST [Vol. LI 



to make definite comparisons as to size. The size of the indi- 

 vidual cells even in one solution varies so greatly that one can 

 only obtain an average of the size and then very roughly. The 

 measurements recorded in the table, and all others made, repre- 

 sent the average size of the larger cells in the solutions as far 

 as it was possible under the circumstances to measure them. 



The results from the other series did not corroborate definitely 

 the results shown for the first series. Therefore, the only con- 

 clusion which can be drawn is, that so far as the present work 

 has shown, variations in density of the water of Great Salt Lake 

 cause no corresponding variations in size of Chlamydomonas 

 cells. 



In every series but one, decided growth of the Chlamydomonas 

 began first in the dilutions about No. 5, and appeared then in 

 order up to No. 1, No. 0, and No. 00, and then down from No. 6 

 to No. 8. Solutions No. 4, No. 3, and No. 2, as a rule, showed a 

 greater abundance of the zoospores, judging from depth of the 

 green color given to the solutions by them. 



The indication is, that water somewhat less dense than that 

 normally present in the lake at its present level is most favorable 

 to development of Chlamydomonas sp. 



Aphanothece packardii does not grow well in the laboratory cul- 

 tures. It was interesting to note that they lost their blue-green 

 color and died in the weakest solutions first ; this condition follow- 

 ing regularly up the series to the most dense solutions. This species 

 gave us no further results. Whether this failure was due to 

 the weak solutions being particularly unfavorable to the alga, 

 or whether it merely indicates that this form is difficult to keep 

 under laboratory conditions, is not certain. Tlie latter seems 

 the more likely conclusion. 



The diatoms recovered from the dense waters, on being trans- 

 ferred to the weaker solutions in the laboratory, multiply read- 

 ily and actually tl^rive, giving large masses of the characteristic 

 brown growth. In every series, after about a month in the labo- 

 ratory, solutions No. 1 and No. 2 show a very few live forms 

 which soon die. In No. 3 a few persist ; but in No. 4, No. 5, No. 

 6, and No. 7, they appear abundantly aiul continue to multiply 

 indefinitely. In No. 8 the live plants an^ acain not very numer- 

 ous. These observations are in compi- tf liai in(>n\ with the state- 

 ments" that the diatoms are foiiml in ^nmr ahnndance in the 

 shoaler, fresher waters near to the mouths of the i-lvers emptying 

 into the lake. They are reported to be especially numerous on 



