

1909] COPELAND— PERIODICITY IN SPIROGYRA 25 



dition, both in the laboratory and in the field, since October, 1905, 

 but no trace of fruiting material has been found. 



11. Notes taken in the field and supplemented by those in the 

 laboratory offer overwhelming evidence in support of the view that 

 the phenomenon of conjugation results not so much from external as 

 from internal conditions. 



1 



12. The writer therefore concludes that Spirogyra has definite 

 periods of growth and activity. 





Clark University 

 Worcester, Mass. 



LITERATURE CITED 



1. Bennett and Murray, A handbook of cryptogamic botany 266. London. 

 1889. 



2. Fritsch, F. E., Problems in aquatic biology, with special reference to the 



study of algal periodicity. New Phytol. 5:149-169. 1906. 



3- Hassall, A. H., A history of the British freshwater algae. London. 1857. 

 4« Hoyt, W. D., Periodicity in the production of the sexual cells of Dictyota 



dichotoma. Bot. Gazette 43:383-392. 1907. 

 5. Petit, P., Spirogyra des environs de Paris. 1880. 

 o. Vaucher, J. P., Histoire des conferves d'eau douce. 1803. 

 7- West, G. S. and W., Observations on the Conjugatae. 'Annals of Botany 



12:29. 1898. 



8. Williams, J. Lloyd, Periodicity in the sexual cells in Dictyotaceae. Annals 

 of Botany 19:533. 1905. 



9. Wood, H. C, Contribution to the history of the freshwater algae of North 



America. Smithsonian Report. 1874. 

 10. Wolle, F., Freshwater algae of the United States. Bethlehem, Penn. 1887 . 



