408 Canadian Record of Science 



found in fruiting condition. Copeland concludes, 

 from notes taken in the field and supplemented by 

 work in the laboratory, that conjugation results not so 

 mucn from external as internal conditions. He, there- 

 fore, concludes that Spirogyra has definite periods of 

 growth and activity. 



In regard to. the possibility of satisfactory cultures 

 in tap-water, the advantage of a certain amount of 

 shade and the beneficial effects of an association with 

 other forms, especially GEdogonium, my results agree 

 fully with those of Copeland. 



Fritsch and Rich, in their "Preliminary Observa- 

 tions on Spirogyra," base their theories on observation 

 of this genus under a natural environment. 



Of the species examined, some appeared to be 

 purely vernal or else to exhibit both a vernal and an 

 autumnal phase with an intervening period of scarcity 

 or complete disappearance. The factors for the dis- 

 appearance of Spirogyra after the vernal phase are 

 enumerated as follows : 



(a) The increase in the intensity and duration of 

 the light. 



(b) The increase in the. temperature of the water 

 and the consequent diminution of the amount 

 of dissolved gases in the water. 



(c) The gradual concentration of the salts dis- 

 solved in the water owing to the heat and the 

 the lack of rain-fall in a normal summer. 



(d) The increase in the amount of higher vegeta- 

 tion present. 



The autumnal appearance of certain species of 

 Spirogyra may be due, they think, to the influence of 

 certain combinations of external factors causing a 

 small number of zygospores to germinate. In the 

 absence of these conditions there may be no autumnal 

 phase. Abnormal meteorological conditions may bring 

 about abnormal absence or occurrence of Spirogyra. 



