1909] COPELAND— PERIODICITY IN SPIROGYRA 13 





with the exception of the culture medium. In this group attempts 

 were made to repeat the experiments while using tap instead of pond 

 water. As a result, it was found that the aquaria with tap-water were 

 as satisfactory, and, in most cases, much more so than those with 

 pond water. Hence tap- water aquaria were used as controls. 



It is well to note concerning this point that the tap- water was from 

 reservoirs which were in turn supplied by small brooks and surface 

 drainage. In many cases the pond water was taken from ponds 

 supplied b.y brooks which drained the reservoirs just mentioned. 



I next tried a group of experiments for the purpose of fixing some 

 value to the use of plant food solutions for the investigation at hand. 



most 



was employed in a great many experiments 

 taneously with Knop's. In comparing aqua 



solutions, no general rule ronlH he establish 



On the whole, how- 



ever, the writer is inclined to favor at least a weak food solution. 

 Knop's solution as low as o . 04 per cent, gave favorable results. 



A long list of experiments was prepared in which rain and distilled 

 water were used ; and in others melted snow. Some of these were not 

 disturbed after being placed in their respective windows. Others 

 were left in these media for periods varying from one to ten days 

 and then changed to a weak food solution (usually 0.05 per cent.), 

 and this was raised by degrees to o. 2 per cent, where it was allowed 

 to remain. In this group care was taken to select Spirogyra from 

 different localities. Specimens were obtained from swift water, from 

 slow-running brooks, and from small quiet pools and ponds where very 

 httle disturbance was possible. Notes on these experiments show 

 that no particular advantage was gained by using these media. 



From the first the aquaria located in the southeast windows were 

 shorter lived than either of the other sets of aquaria. It will be 

 remembered that the only difference in conditions was a slight differ- 

 ence in temperature plus a difference in light intensity. Experiments 

 were now conducted in order to try the effect of shading the cultures. 

 lssue P a Per of different colors was used for this purpose. The best 

 results were obtained when the aquaria wpty> ^nt shaded above the 

 surface of the water. After scores of e 



periments 



started 



