1909] COPELAND— PERIODICITY IN SPIROGYRA 23 



for either the large or small sizes, although all sizes were usually 

 arranged at the same time. In dozens of test-tubes two-thirds full 



media 



four 



factory. In three large aquaria of about forty liters each no successful 

 cultures were made, although frequently attempted. 



An attempt was repeatedly made to grow Spirogyra in some of the 

 larger aquaria after a species had died in it and without renewing the 

 culture media. In every instance where this was tried the plant 

 died down in a few days, showing that the solution contained a toxin 

 injurious to Spirogyra. It is left as an open question whether a mass 



of Spirogyra in nature dies from the accumulation of this same destruc- 

 tive element. 



Aside from the twelve species herein described, there was still 

 another which has been kept under observation since early in the fall 

 of 1905. It is a large form and was found growing in rather large 

 bright-green patches in the 

 one to three miles apart. When first found, a few aquaria were 



running 



remained 



indication of decline. This is an ordinary aquarium of about 10 liters ; 

 it is kept well covered and for that reason very little evaporation takes 



place. 



Oedog 



and green hydra have lived in the aquarium from the beginning. 



7 



the season of 1906. In concluding, I wish to call attention to the 



filament 



aquarium; and furthermore, that none was found at any of the 

 three brooks mentioned, although in one case the plant was very 

 abundant. It is also remarkable that there has not been a time 



obtained. 



first wh 



duri 



In addition it ought to be said that this study was continued 



same 



e same conditions and methods of study. This second year's 



observations and experiments did 



the 



ary enough from 



previous year to warrant any change in the conclusions above 

 given. 3 & 



