THE INFLUENCE OF TEMPERATURE 61 



shock-effect, the changes were made at the rate of from i to ioC. per 

 minute. At the end of each experiment the velocity of streaming was 

 noted at room-temperature, in order to determine whether any internal 

 change had been produced. Whenever this occurs the results are of 

 course useless for comparison. Prolonged exposure to a moderately 

 high temperature ultimately exercises a depressant influence on streaming 

 in spite of its primary direct acceleration. This may be somewhat 

 analogous to the effect of a high temperature in inducing lassitude in 

 warm-blooded animals. Thus, after being at 37 C. to 38 C. for three 

 days, Char a fragilis shows slow streaming, becoming active in a few 

 minutes at 20 C., while Elodea shows none, although fairly active streaming 

 appears after five to fifteen minutes at 20 C. A day's exposure to a tem- 

 perature of 40 C. to 45 C. suffices to cause a permanent stoppage of 

 streaming and ultimately death in Char a, Nitella, Elodea, Spirogyra, 

 Sagittaria, Tradescantia, Lepidium, pollen-tubes, and root-hairs. 



Similarly, prolonged exposure to low temperatures may cause a com- 

 plete or nearly complete stoppage of streaming. Thus, after six hours at 

 oC. to 0-2 C., only very slow streaming is shown by Chara, Nitella, and 

 Elodea, while after two days only the larger axial cells of Nitella exhibit 

 very slow streaming, the latter becoming active or nearly active in all or 

 nearly all the living cells after a quarter of an hour at 20 C. In the first 

 two plants a stoppage of streaming indicates that the limit of resistance is 

 nearly reached or even surpassed. A change of temperature may directly 

 affect the rate of streaming by changing (i) the viscosity of the protoplasm, 

 (2) the energy consumed in streaming. Only a fraction of the energy of 

 respiration is ever used in streaming, and since every protoplast is capable 

 of regulating and proportioning its own activity, it does not necessarily 

 follow that an increased respiration involves a proportionate increase in the 

 energy of streaming. As the temperature rises, however, the viscosity 

 decreases less and less for each degree, whereas the increments of velocity 

 progressively increase between 10 C. and 30 C. It follows, therefore, that 

 the increased activity of streaming is mainly due to the diversion of an 

 increased fraction of the respiratory energy into this channel. Above 30 C., 

 however, the successive increments of velocity for each rise of tempera- 

 ture progressively decrease, and the influence of the changes of viscosity 

 becomes more prominent. The almost immediate stoppage occurring 

 at temperatures above 55 C. to 60 C. is the result of partial coagulation, 

 but the more gradually produced cessation taking place at 45 C. to 

 55 C. is probably the result of a functional derangement of the motor- 

 mechanism. 



In all cases it must be remembered that the regulatory mechanism 

 may come into play so that the tempo at first assumed may not be the 

 same as that exhibited after longer exposure. 



