68 PHYSIOLOGY OF STREAMING MOVEMENTS 



probably the result of the cumulative depressant influence of the low 

 temperature upon the vital activity of the cell as a whole. 



A similar stoppage of streaming is produced by prolonged exposure 

 to temperatures lying just above the freezing point (o C. to i C.), six to 

 ten hours usually sufficing in the case of Trianea, Tradescantia, and Vallis- 

 neria, but periods of one to two days being required by Chara and Elodea, 

 and three to four days by large axial cells of Nitella. 



SECTION 27. Influence of Temperature during Anaerobic 

 (intramolecular) Respiration. 



The hot chamber used for these experiments was provided with exit- 

 and entry-tubes for gases, and the cover-slip after its rim had been smeared 

 with vaseline was sealed with wax, melted shellac, or plaster of paris and 

 shellac, according to the temperature. The same precautions as previously 

 mentioned were used to obtain perfectly pure oxygenless hydrogen. 



When green cells are examined, their power of photosynthesis may 

 be temporarily inhibited by etherization. Streaming is, however, also 

 affected, weak doses accelerating and stronger doses retarding it. Doses 

 sufficient to cause a slight retardation of streaming in Elodea usually 

 inhibit the power of CO^-assimilation, so that streaming ceases in hydrogen 

 in about the same time whether the preparations are kept in darkness 

 or exposed to light. 



Removal of the ether vapour by a fresh current of hydrogen may 

 shortly be followed by a resumption of CO 2 -assimilation and a recom- 

 mencement of streaming, if the exposure has been short. With more 

 prolonged exposures, recovery may not take place in hydrogen although 

 it may in air, while with still longer exposures the power of recovery is 

 entirely lost. Unfortunately streaming soon ceases in Elodea in the absence 

 of free oxygen, while Chara and Nitella are soon fatally affected by doses 

 of ether sufficient to produce the required effect. 



Above 38 C., however, Chara and Nitella cease to evolve oxygen, 

 and hence above 40 C. the power of CO 2 -assimilation must be entirely 

 or almost entirely in abeyance, so that at high temperatures chlorophyllous 

 cells yield in light approximately similar results to those given by the 

 colourless rhizoids. 



In general it may be said that between 5 C. and 45 C. the influence 

 of a rise or fall of temperature upon the velocity of streaming is both 

 absolutely and relatively less pronounced than when aerobic respiration 

 is fully active, the cells behaving as if in a semi-dormant condition. This 

 is probably because the temperature affects the katabolism and hence the 

 liberation of energy to a relatively less degree than in the presence of 

 oxygen. 



