



1909] COPELAND— PERIODICITY IN SPIROGYRA n 



in fruit from Juki until October. One species fruited in April and 



May and agJon in October. 



Since 1880 a number of papers relating to Spirogyra have appeared, 

 but only a few of them give any facts that can be used in a study of 

 periodicity. Bennett and Murray (i) write: " Germination some- 

 times takes place while still in the mother cell; but most commonly 

 both filaments perish after conjugation, with the exception of numer- 

 ous zygospores which fall to the bottom. These remain dormant 

 through the winter .... germinating in the spring .... instances 

 are recorded of filaments persisting through the winter. Hofmeister 

 states that the growth of Spirogyra is intermittent." 



The following case is reported by W. and G. S. West (7): "We 

 have melted out of the ice from Micham Common, Surrey, excellent 

 examples of Spirogyra catenae] or mis in conjugation, the vitality of 

 which was in nowise impaired." 



The few scattered remarks given include all the notes the writer 

 has been able to gather from papers published before 1905. In this 

 year a few papers appeared which had a more direct bearing on the 

 subject at hand. These seem to be the pioneer publications on the 

 subject of algal periodicity. In indicating some of the "problems of 

 aquatic biology" Fritsch (2) calls attention to the fact that different 

 bodies of water, often far apart, will have the same dominant and 

 often the same subordinate vegetation ; also that a plant may be very 

 abundant one month and almost, if not entirely, absent the next 

 month. An intimate relation was found to exist between the relative 

 abundance of an alga and its period of reproduction; the formation 

 of the sex organs frequently preceding the disappearance or dimin- 

 ished abundance of a given species. Fritsch writes: "In some 

 cases no doubt these features (maximum abundance and period of 

 reproduction) are influenced by the periodically recurring factors 

 such as the rise of temperature and the increase in the intensity of 

 light in the spring; so that the maximum abundance and period of 

 reproduction are definite phenomena." 



Another paper on the subject of algal periodicity appeared in 

 905- So far the publications mentioned have had to do only with 

 freshwater algae; for that reason it is well to call attention to studies 

 made on marine forms. While at work on Dictyotaceae, Williams 



1 



