THE INFLUENCE OF FREE OXYGEN UPON STREAMING 39 



Carefully sealed preparations of end-cells of Chara> which were exposed 

 to bright light for one minute daily, remaining living and exhibiting slow 

 streaming until the thirtieth to thirty-sixth day, streaming ceasing on the 

 thirty-sixth to fortieth day. Death is here, however, more the result of 

 mal-nutrition than of a deficiency of oxygen. Slide preparations of Chara 

 and Nitella, thinly ringed with boiled linseed oil, showed slow but quite 

 perceptible streaming after twenty-eight days in darkness, the streaming 

 quickening in ten to thirty minutes on re-exposure to light 1 . Farmer 2 

 states that streaming ceases or becomes extremely slow within half an 

 hour, when cells of Nitella are kept in darkness in a current of hydrogen. 

 If then exposed to light, streaming became active in one to two minutes, 

 but on again darkening was nearly or quite arrested in five to seven 

 minutes. According to Farmer, this shows that the oxygen produced by 

 carbon dioxide assimilation in two minutes is used up by respiration in 

 seven 3 . These conclusions are, however, hardly trustworthy, since slow 

 streaming may be present after a whole day in darkness in a stationary 

 atmosphere of pure hydrogen, although in a. slow current of hydrogen 

 streaming may be reduced to the same low ebb after one to three hours' 

 darkness at 20 C. 



It has previously been shown that the oxygen contained by a cell is 

 evolved more rapidly in a current of H, than in an atmosphere of H or N, 

 and much more rapidly than if immersed in oxygenless water 4 . This fact 

 was overlooked by Farmer, and as a matter of fact fifteen to thirty minutes' 

 daily exposure to bright light sufficed to maintain moderately active 

 streaming, and a total daily exposure of three to five minutes maintained 

 slow streaming in cells of Chara and Nitella enclosed in small air-tight 

 glass cells containing at the outset 95 per cent. N and 5 per cent. CO 2 . 



Clarke (1. c.) found that streaming commenced in cells of Nitella at an 

 oxygen pressure of from 1-2 to 2-8 mm. of mercury, i. e. in the presence of 

 yfr to T ^-Q- of the normal amount of oxygen, but no mention is made of the 

 time required for complete cessation, and in fact it is doubtful whether 

 any such ever occurred. 



In considering these observations, two fertile sources of error must be 

 borne in mind. Firstly, when cells exhibiting very slow streaming are 

 suddenly exposed to light and examined, the movement is usually missed 



1 After prolonged slow streaming all the larger granules, and many of the smaller ones, are 

 deposited, leaving the streaming layer almost clear, and making slow streaming correspondingly 

 difficult to distinguish immediately. 



a Ann. of Bot., 1896, Vol. x, p. 288. 



3 Bonssingault (Agron., Chim. agricole, &c., 1864, T. m, p. 378 ; 1868, T. IV, p. 286) and Holle 

 (Flora, 1877, p. 187) state that chlorophyllous cells can decompose tinder optimal conditions from 

 15-30 times the amount of carbon dioxide that they exhale in the same time in darkness, and thus 



-'two minutes' photosynthesis would produce sufficient oxygen for 30-60 minutes' aerobic respiration. 



4 Ewart, Journ. Linn. Soc., 1896, p. 42. 



