88 PHYSIOLOGY OF STREAMING MOVEMENTS 



10 per cent, of copper sulphate, owing to the fact that the ectoplasmic 

 membrane of this plant is impermeable to the salt in question, but this 

 appears to be an exceptional case 1 . 



The action of a metallic poison is markedly influenced by temperature, 

 the minimal poisonous dose being lower at a high temperature than at 

 a low one, even when a small range of temperature is used, 5 to ioC, 

 15 to 20 C, 25 to 30 C. This is because metabolism is more active 

 at the higher temperature, and hence the interference of the poison is 

 more pronounced. For this reason also, the time of exposure necessary 

 to produce a fatal effect is much shortened at the higher temperature. 

 If the effects at 15 to 20 C. are compared with those at 30 C. to 40 C. 

 the difference is still more pronounced. This is partly due to the in- 

 creased dissociation at the higher temperature, and hence the larger 

 percentage of the free ions upon which the poisonous action depends. 



SECTION 39. Electrical Stimuli. 



Becquerel and Dutrochet 2 were the first to show that an electric 

 current caused a temporary stoppage of streaming in Chara and Nitella^ 

 the result being dependent on the strength of the current but not upon 

 its direction. Jurgensen 3 found that weak currents caused a retardation 

 and ultimate complete stoppage of streaming in Vallisneria spiralis^ and 

 that stronger currents produced an immediate permanent cessation. 

 Kiihne 4 observed in the case of hairs of Tradescantia exposed to constant 

 currents that the protoplasm accumulates at the positive pole, and that 

 owing to electrolytic action the cell-sap at this end turns red and acid ; 

 but, at the negative end, alkaline and green. He also noticed that 

 under the influence of induction shocks the protoplasm aggregated in 

 masses or balls, from which condition recovery was possible. 



Velten 5 found that weak induction shocks or weak constant currents 

 caused a retardation of streaming, and that after the latter had nearly 

 ceased under exposure of very limited duration, from one to two hours 

 were required for complete recovery. 



Klemm (1. c., pp. 24 seq.) has shown that the nucleus is killed first, 

 as is evidenced by its swelling and absorbing pigments, while the large 

 vacuolated masses into which the protoplasm separates may exhibit 

 streaming for as long as four hours, although they contain no nucleus. 

 Similarly streaming may continue after the nucleus has been killed. 



Cf. Pfeffer, Pflanzenphysiologie, 2. Aufl., Bd. II, p. 342. 

 Ann. sci. nat., 1838, ii. ser., T. ix, p. 80. 



Stud, des physiol. Inst. zu Breslau, 1861, p. 87. Cf. also Sachs, Physiologic, pp. 74 seq., 

 for the works of Briicke, Heidenhain, &c. 



Unters. iiber das Protoplasma und die Contractilitat, Leipzig, 1864. 

 Sitzungsb. d. k. Akad. d. Wiss. zu Wien, 1876, Bd. LXXIII. I, p. 350. 



