1909] COPELAND— PERIODICITY IN SPIROGYRA 21 



May 21-T 



May i-May 15; S. dubia was found 



iflata mention 



that on May 2 this species together with S. calospora and S. catenae- 

 formis were found in fruit at the same time and place. It ought to 

 be noted, however, that S. infiata had passed its period of maximum 

 conjugation and that there were comparatively few filaments of 

 either of the other two species. No S. inflata was found after May 

 4, but from this until May 22, S. catenae} or mis was abundant. In 

 giving a description of the latter species it was noted that this form 

 was found fruiting abundantly at the same time and quite near S. 

 varians. I did not find the two species intermingling, although grow- 



same 



season. 



I am inclined to think that not enough emphasis is given to the 

 fact that the lower plant forms do not have a continuous period of 

 growth, either vegetative or reproductive. In other words, the normal 

 period for either activity is continuous for only a few weeks or months • 

 at most ; it remains a problem of research to show how inclusively this 

 generalization applies to the freshwater algae. For Spirogyra the 

 observations reported in this paper seem to offer overwhelming evi- 

 dence in support of the view, for this region at least, that it is not a 

 perennial plant. I have only a single exception to this conclusion and 

 will speak of it later. A few of the species studied appeared more or 

 less abundantly in the fall ; in this connection S. Hantzschii furnishes 

 a specific example. In a majority of the forty localities kept under 

 observation during 1905-6, several forms of algae succeeded one 

 another in maximum abundance in the course of a year. In only 

 four of the forty places was any trace of Spirogyra found in the fall 

 where it had been in a state of conjugation in the spring. The man- 

 ner in which different species appeared, matured, and conjugated was 

 or most of the forms quite distinct and constant for the several locali- 

 !es. Following the fruiting season the disappearance of the plant 

 took place sometimes suddenly and sometimes gradually. 



It is a well-known fact that vegetative material is very difficult to 



n * y; the same might as well be said of conjugating material. 



nis reason it is difficult to follow any given species with certainty; 



