3*4 



LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



fractional amount of it directed into this channel. The former cause alone 

 is sufficient to more than double the velocity of streaming when the 

 temperature is raised from 2 to 32 C. Nevertheless, the increases of 

 velocity within this range of temperature are much greater than this, and 

 are hence mainly due to an increase in the amount of energy utilized. 

 Above 30 C., however, the influence of the changes of viscosity becomes 

 more prominent, the sudden stoppage occurring at 55 to 60 C. being due 

 to the increase of viscosity which precedes coagulation l . 



The apparently higher optimum temperature observed for streaming 

 as compared with that for growth is largely the result of the lesser duration 

 of the observations in the former case, for prolonged exposure to tempera- 

 tures of from 37 to 40 C. causes streaming to cease or become extremely 

 slow in all the plants examined. In addition, the viscosity of the proto- 

 plasm may permanently increase during prolonged exposure, while the 

 motor-mechanism may also be affected, a change of tempo ensuing. 



The following cardinal points were obtained by various authors 2 : 



The discrepancy in these results is partly the result of the varying 

 duration of the exposure, and is partly due to such factors as age, supply 

 of oxygen, and previous treatment. Thus Ewart 3 obtained values varying 

 only a degree or two from those of Hauptfleisch when the exposures were 

 prolonged, whereas with short exposures an optimum of 40 C. and a 

 maximum of 50 to 60 C. may frequently be obtained. In addition, the 

 optimal and maximal temperatures are lower in young cells of Chara and 

 Nitella than in old ones. Streaming may in fact continue during a short 

 exposure of the latter to a temperature which causes subsequent death. 

 Similarly, the absence of oxygen raises the optimum for short exposures, 

 but lowers the optimum and maximum when the exposure is prolonged 4 . 



1 Ewart, Protoplasmic Streaming in Plants, 1903, pp. 20, 61. 



* Dutrochet, Ann. sci.nat., 1838, pp. 25-7; Memoires, 1837, T. I, p. 561 ; Sachs, Flora, 1863-4, 

 p. 39; Cohn, Bot. Ztg., 1871, p. 723; Velten, Flora, 1876, pp. 210, 214; Klemm, Jahrb. f. wiss. 

 Bot., 1895, Bd. xxvin, pp. 635-6; Hauptfleisch, ibid., 1892, Bd. xxiv. Corti was the first to 

 observe the increase of velocity with rising temperature. See also Klebs, Biol. Centralbl., i88i,Nos. 

 16, 17, 19. 



3 L. c., p. 59. * Ewart, Protoplasmic Streaming in Plants, 1903, p. 68. 



