14 BOTANICAL GAZETTE [January 



it was shaded with black paper; after two weeks, this was changed 

 to yellow; and after another two weeks the shading was not used at 

 all. This was a decided advantage to the aquaria in the southeast 

 windows. While the effect was not so noticeable in the other labora- 

 tories, the results were sufficient to justify this method in all the win- 

 dows. It is not to be understood that tap-water aquaria were the 

 only ones used with a shade. On the other hand, snow, rain, distilled 

 water, and food solutions were used in every case. The same applies 

 to the following series of experiments. 



Up to this time no attention has been given to the substratum, 

 nor to other plants with which Spirogyra is most frequently asso- 

 ciated in its natural habitat. For this group of aquaria soil, debris, 

 and plants, for the most part, were used from the immediate locality 

 from which the specimens were taken. In some cases the soil was 

 first sterilized. 



Among the plants which seemed beneficial to Spirogyra, none 

 proved more helpful than Oedogonium. In fact in every aquaria 

 in which Spirogyra lived for several months or a year, Oedogonium 

 was invariably present and often the predominating alga. The 

 Oedogonium could usually be found attached to the sides of the jar 

 or floating at the surface, thus shielding the Spirogyra from too much 

 sunlight. Chara supplied to the aquaria was helpful so long as it 

 was not too abundant. In some cases where aquaria were thus 

 started, the Chara died out after two or three months and was followed 

 by an abundant growth of Oedogonium, and later by Spirogyra. In 

 the field, masses of Spirogyra were often collected among water cress, 

 but in no case was a good growth of Spirogyra obtained in an aquarium 

 with this plant. A number of jars were supplied with oak leaves 

 taken directly from the trees where they had remained all winter. 

 To other aquaria pieces of charcoal were added. Both of these 

 factors seemed beneficial and in 



most 



Spirogyra were obtained which lasted until conjugation had taken 



place. 



Spirogyr 



Field-work was begun early in April. At this time 400 aquaria 

 o all sizes were in use and too of them contained excellent cultures 

 of Spirogyra which had been under cultivation for two months. On 



