40 PHYSICS OF STREAMING 



at first, and hence seems to commence as the eye is focussed upon the cell. 

 Secondly, the merest trace of certain gases (HC1, As H 3 , SO 2 ) in the hydro- 

 gen employed will affect the accuracy of the results. Indeed, the injurious 

 effect of currents of hydrogen on Char a and Nitella noted by certain 

 observers is simply the result of the presence of poisonous impurities. 



For example, if a current of hydrogen obtained from commercial zinc 

 and pure dilute sulphuric acid is passed over darkened cells of Chara and 

 Nitella, streaming ceases in one to two hours in the latter case, and in three 

 to ten hours in the former. 



If the tubes are clamped and the current stopped just before cessation, 

 the streaming quickens somewhat, though still in darkness. The stoppage 

 is probably partly due to the poisonous impurities in the hydrogen, and the 

 recommencement or quickening to the presence of a trace of oxygen, for 

 in deoxygenated hydrogen no such quickening occurs. In absolutely 

 pure hydrogen, moreover, although streaming is reduced to a very low 

 ebb, it does not entirely cease in these plants a . 



On the other hand, thickly ringed preparations of Chara and Nitella 

 immersed in oxygenless water in darkness cease to show streaming in two 

 to four days, and die in from three to five. This is, however, not so much 

 due to the absence of oxygen as to the accumulation of the products of 

 intramolecular respiration (CO 2 , and possibly traces of organic acids or 

 alcohol). In thinly ringed preparations kept in air the carbon dioxide and 

 alcohol diffuse outwards, and hence the cells remain living for weeks in 

 darkness, whereas if immersed in carbon dioxide or in air saturated with 

 alcohol vapour this cannot occur, and the cells die in two to five days. 

 Cells of Nitella and Chara cease to show streaming within fifteen minutes 

 in an atmosphere containing 95 per cent, carbon dioxide and 5 per cent, 

 oxygen, and are killed in less than an hour even if illuminated. 



It is owing to the facts just mentioned that Ritter 2 has obtained con- 

 tradictory results to my own, and to the later one by Kuhne 3 , who found 

 that streaming may continue in Nitella for a month in the absence of free 

 oxygen, and concluded that this is due to the presence of an internal store 

 of oxygen. Ritter, on the other hand, states that streaming ceases in four 

 days in Chara stelligera, and in two to three days in Nitella, the cells 

 remaining living a day longer. 



There are, therefore, almost as many contradictory results as there 

 have been investigators, and as instances of the caution necessary in 



1 The hydrogen used for my own test experiments was obtained from nearly pure zinc and pure 

 sulphuric acid, and was purified by passing through solutions of Na 2 CO 3 , Ag NO 3 , KHO and alkaline 

 pyrogallol, all in U tubes containing pumice-stone. The surface of acid in the generator was covered 

 with liquid paraffin, and all connexions, as well as the entire purifying apparatus, were placed under 

 water covered by liquid paraffin. 



' Flora, LXXXVI, 1899, pp. 329-60. 3 Zeitschr. f. Biol., 1897, Bd. xxxv, p. 43; 1898, p. i, 



