Brown : Algal periodicity 237 



November it disappeared, not appearing again until the middle of 

 the following April. It then became rather abundant, reaching its 

 maximum in the first half of May. On May 18 it was fruiting 

 abundantly. About the first of June, it had become very rare in 

 most places, entirely disappearing in some. 



The causes of this periodicity of Ocdogonium are not easy to 

 explain ; only a few facts can be pointed out that probably had an 

 influence. The increase in the amount of Oe. crassinsculiim in 

 November was not very great. Doubtless a good portion of this 

 passed the summer in a sort of resting condition — the filaments 

 growing but little — then, when rains came in November, increas- 

 ing the amount of water in the pond, there was growth. Follow- 

 ing this time, the temperature became too low for much growth 

 and the alga became more rare, yet a relatively small amount per- 

 sisted throughout the winter in a resting state. When heavy rains 

 came in March, accompanied by warm weather, there was a rapid 

 growth for two or three weeks. As the temperature of the water 

 became higher and the light more intense, the alga was caused 

 to pass from a vegetative to a fruiting state and after fruiting it 

 began to disappear rapidly. Klebs* (1896) found in experiment- 

 ing with Ocdogonium that increasing the intensity of light would 

 tend to cause an increase in the production of sexual organs. 



Bulbochaete crenulata appeared in pond no. 1 about November 

 23i and persisted during the winter in small quantity, growing but 

 little. About the first of May, it had become slightly more abun- 

 dant, was growing somewhat, and bearing sexual organs. Later 

 in May it disappeared. On July 31 a small amount was found 

 attached to grass in the upper end of the larger of the water-works 

 ponds. It was in a vegetative state and did not appear to be grow- 



ing much. 



The Chaetophorales were tolerably abundant in the ponds and 

 streams studied and rather generally distributed, the genera Chaeto- 

 phora and Draparnaldia being the most abundant. 



Representatives of but two genera were found belonging to 

 the family Ulotrichaceae ; these were Ulothrix and Stichococcus. 

 Ulothrix aequalis appeared in pond no. I about the middle of 



1896. 



*Kle"bs. Die Bedingungen der Fortpflanzung bei einigen Algen und Pilzen. 



