98 PHYSIOLOGY OF STREAMING MOVEMENTS 



cell-sap. The ectoplasmic membrane is, however, often the last part of the 

 cell to die, and this is probably due to its having acquired a greater resis- 

 tant power to external agencies, in adaptation to its more exposed situation 

 and more changeable environment. 



If cells are subjected to very weak currents l for prolonged periods of 

 time, the course of events may be slightly different, for the endoplasm of 

 cells of Char a and Nitella may still show slow creeping streaming after the 

 ectoplasm has shown signs of being fatally affected, such as partial local 

 retraction, irregular arrangements of chloroplastids, and appearance of gaps 

 between them, collapse of chloroplastids, and protrusion of the contained 

 starch grains. The cells then showed no power of CO 2 -assimilation when 

 examined by means of the Bacterium method. In such cases the order of 

 death appears to be (i) nucleus, (2) ectoplasm, (3) ectoplasmic membrane, (4) 

 endoplasmic membrane, and (5) endoplasm, whereas with stronger currents 

 the order appears to be in the uninucleate cells of Tradescantia, Urtica, 

 Trianea, &c., (i) nucleus, (2) endoplasmic membrane, (3) endoplasm, (4) 

 ectoplasm, (5) ectoplasmic membrane. 



Streaming may often persist after the power of CO 2 -assimilation has 

 been temporarily or permanently lost. On the other hand, according to 

 Kny 2 , after passing a 60 volt constant current, or induction currents giving 

 a 2 cm. spark, through cells of Nitella and Spirogyra, an active power of 

 CO 2 -assimilation could be detected in them by the Bacterium method for 

 one to three days afterwards, although streaming had permanently ceased, 

 the chloroplastids become disorganized and the protoplasts retracted. Kny 

 indeed concluded that the effect of very strong electric currents was to 

 increase the assimilatory activity of the chloroplastids, although killed, 

 altered in shape, and more or less completely disorganized. It seems, how- 

 ever, hardly possible that a vital function could continue with increased 

 activity in a dead cell, and, as a matter of fact, these remarkable results 

 were due to the use of impure cultures and unringed preparations. The 

 dying or dead cells evolve nutritious substances which attract facultatively 

 anaerobic Bacteria, and even aerobic ones in the presence of traces of 

 oxygen derived from without. In no case does a dead cell, when properly 

 tested, exhibit the faintest power of CO 2 -assimilation 3 . 



It is not impossible that weak constant currents may increase the 

 activity of CO 2 -assimilation in living cells, either directly or as an after- 

 effect. No positive results have, however, been obtained as yet, and 

 certain observations of my own point to the contrary conclusion. 



1 A current of unit-voltage may fatally affect a cell of Nitella in from a few minutes to half an 

 hour, if the external resistance is low, and one of a to 3 volts in less than a minute. Stronger 

 currents are required with leaves of Elodea and Vallismria unless strips of leaf-cells are employed. 



9 Ber. d. deut. hot. Ges., Bd. xv, p. 399. 



3 Ewart, Bot. Centralbl., 1898, Bd. LXXV, No. 2. 



