68 



BRITISH CHAEOPHYTA. 



Darkness on the one hand and intense light on the 

 other have the effect of retarding the flow, a weak 

 light being apparently the most favourable condition. 



Cyclosis was found to continue both in species of 

 Chara and of Nitella for some weeks in the entire 

 absence of free oxygen in the surrounding water. 

 The cells of Charophytes appear to be unusually 

 resistant of the action of carbonic acid. 



The results of many experiments as to the effect 

 of acids, alkalies and alkaloids on the flow are 

 detailed by Dr. Bwart. Dilute solutions of nitrate 

 of potash and chloride of soda considerably retard the 

 flow. Dilute alcohol and anaesthetics, such as ether 

 and chloroform, tend to accelerate, while strong solu- 

 tions retard the flow. 



Temporary suspensions of the flow are found to 

 occur as the result of shocks from various causes 

 such as sudden immersion in a strong alkaline solution 

 or mechanical disturbance. 



In the larger elongated cells gravity was found 

 appreciably to affect the rate of flow. In a cell of 

 a Nitella the mean velocity of the upward stream at a 

 temperature of 17*6° C. was measured to be 1'99 and 

 1"96 mm., as against that of the downward stream 

 of 2"13 and 2"15 mm. per minute. 



The rotatory movement observable in the ohloro- 

 plastids carried along in the flow is apparently due to 

 mechanical causes. 



As regards the effect of magnetic and electric 

 stimuli. Dr. Ewart in stating his conclusions as to 

 streaming in plants generally, remarks: "The strongest 

 magnetic force used exercised little or no direct effect 

 on streaming, although a pronounced secondary effect 

 is produced on prolonged exposure as the result of in- 



