THE INFLUENCE OF FREE OXYGEN UPON STREAMING 43 



germinate in the absence of oxygen. Hence it still remains to be decided 

 whether the anaerobiosis of Chara and Nitella is always merely temporary 

 and facultative, or whether these plants, under special conditions of nutri- 

 tion and environment, can be converted into completely anaerobic sapro- 

 phytes. An interesting point is that in several cases cells remained living 

 for some time on re-exposure to light and air, especially if fed with dilute 

 glycerine, although their relatively more aerobic chloroplastids showed 

 signs of fatal injury, producing no starch, and ultimately becoming com- 

 pletely bleached. 



In other cases, the admission of air causes merely a slight temporary 

 quickening of streaming, soon followed by its complete cessation. Appar- 

 ently the entrance of free oxygen so disturbs the anaerobic metabolic 

 equilibrium as to cause rapid death, probably much in the same way that 

 free oxygen causes the death of obligate anaerobes. 



That slow streaming does actually continue during the whole time 

 that oxygen is absent, and does not merely commence at the moment of 

 examination, is easily proved by arranging so that the cells can be observed 

 under a low power before oxygen is admitted, and since the chloroplastids 

 have temporarily or permanently lost the power of CO 2 -assimilation, the 

 short exposure to light during examination does not cause any production 

 of oxygen by photosynthesis. 



There is only one other possibility to consider, which is, whether the 

 cells of Chara and Nitella may contain a store of occluded oxygen, or of 

 oxygen held in a state of loose chemical combination, which could be 

 utilized for the maintenance of the minimal amount of aerobic respiration 

 necessary to preserve the vitality of an aerobe. It has already been shown 1 

 that certain bacteria do actually possess a pigment which has the power of 

 occluding oxygen, and that they are able to respire for a short time at the 

 expense of this oxygen in the absence of any external supply. The fact 

 that the absorbent substance is coloured is a mere accident, and hence 

 Chara and Nitella might easily have a similar power of storing or occluding 

 oxygen, although they produce no such pigments as are formed by these 

 bacteria. 



That neither the calcareous incrustation of Chara nor the cell-wall 

 has any such property is easily proved by the use of test-bacteria, and by 

 means of solutions of reduced indigo-carmine (1. c., p. 126). Similarly, 

 the expressed sap contains normally only a small trace of dissolved oxygen, 

 and after the cells have been kept in darkness and in pure hydrogen for an 

 hour or two, this trace entirely disappears. The latter can be shown by 

 placing cells over a gas chamber in the usual manner, but with a strip of 

 glass crossing underneath them. On applying pressure the cell bursts, 



Ewart, Journ. Linn. Soc., 1897, Vol. xxxiil, p. 123. 



