286 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



are, however, not affected injuriously by the existence of streaming move- 

 ment. Although streaming may favour nutrition and metabolism, it does 

 not necessarily make them especially pronounced ; and, on the other hand, 

 streaming may be inhibited by treatment with chloroform, which does not 

 stop and may even accelerate respiration, and it may continue under partial 

 pressures of oxygen which do not suffice for the formation of chlorophyll 

 in etiolated chloroplastids 1 . 



With the exception of the peripheral layer, all the rest of the protoplasm 

 shows streaming or is capable of it. In the case of Chara and Nitella 

 the non-motile peripheral layer is thick and contains almost all the chloro- 

 plastids embedded in it, whereas in Elodea and Vallisneria when streaming 

 is active all the chloroplastids are carried with the stream and only the 

 extremely thin ectoplasmic membrane adhering to the cell-wall is at rest. 

 Hanstein was, however, incorrect in supposing that the entire protoplast 

 turned round within the cell 2 . When the protoplast is plasmolysed 

 streaming may continue, but particles adhering to the ectoplasmic membrane 

 remain at rest. Hence the absence of movement in the peripheral layer 

 is not due to its contact with or adherence to the cell-wall. In certain 

 cases, however, plasmolysed portions connected by a thread appear to show 

 a slight rolling movement, but this does not appear to be directly connected 

 with the streaming movement, and is possibly the result of the action of 

 surface-tension or gravitational forces 3 . In the case of Chara and Nitella 

 it is easy to see that the peripheral, well-defined, and permanent layer of 

 ectoplasm acts like a gelatinous solid which is incapable of being set in 

 motion by the friction of the moving layers. Similarly the cohesion of 

 the protoplasm of streaming cells of Elodea and Vallisneria probably 

 increases towards the periphery, so that when the rapidity of streaming 

 rises, more of the ectoplasm is brought into motion until only the extreme 

 peripheral layer which has the properties of a fixed membrane remains at 

 rest. The fact that the vacuolar membrane moves with the plasma and 

 sets the cell-sap in motion shows that either the ectoplasmic membrane 

 is more solid in character or that it is thickened by the attachment of more 

 highly cohesive layers of ectoplasm 4 . In the case of many pseudopodia 

 and in that of the external plasma of Diatoms, the water and peripheral 

 layers of protoplasm appear to move in the same direction, so that it is 

 possible that cells may exist in which the ectoplasmic membrane of 

 dermatoplasts may be capable of streaming movement. Apart from the 



1 Ewart, Journ. of Linn. Soc., 1897, Vol. xxxi, p. 566. 



a Hanstein, Bot. Abhdlg., 1880, Bd. iv, Heft ii, p. 15. Cf. Velten, Flora, 1873, p. 97 ; Hof- 

 meister, Pflanzenzelle, 1867, pp. 35, 45; Pfeffer, Plasmahaut u. Vacuolen, 1890, p. 269; Wigand, 

 I.e., p. 194; Hermann, Studien iiber die Protoplasmastromung bei d. Characeen, 1898, p. 24; 

 Ewart, Protoplasmic Streaming in Plants, 1903, p. 6 seq. 3 Ewart, I.e., p. 9. 



* Velten, I.e., p. 98; Hofmeister, I.e., p. 43; Berthold, I.e., p. 122; Rhumbler, Zeitschr. f. 

 allgem. Physiologic, 1902, Bd. I, p. 304. 



