AMEBOID MOVEMENT 97 



slowly than the middle of the stream, and the effect of this is that 

 the outer edge of the vacuole is dragged along with the moving 

 endoplasm. This is an important observation and from it Ewart 

 concludes that the energy which produces the streaming movement 

 must be liberated, not at the boundary between the ectoplasm and 

 the endoplasm, nor at that between the endoplasm and the vacuole, 

 but within the endoplasmic stream itself. In this conclusion 

 Ewart is undoubtedly correct, for as a physical phenomenon, no 

 other conclusion is at present possible. 



Other experiments made upon the velocity of streaming in 

 plant cells indicate that the streaming process obeys the laws of 

 physics. The velocity varies with the proportion of water present 

 in the endoplasm, the more water, the faster the streaming 

 (Ewart, '03). The effect of temperature on streaming, .noted 

 first by Corti ('74), and studied by Velten, ('76), Schaefer ('98), 

 Ewart ('03) and other writers, is also such as would be expected 

 if the endoplasm were a simple physical fluid. 



The rotational streaming in plant cells, such as those of Chara, 

 is very similar to the rotational streaming in paramecium and 

 numerous other ciliates. In these organisms it is often called 

 cyclosis. A paramecium differs, however, from a plant cell 

 exhibiting rotational streaming in that no central vacuole is 

 present. This space in paramecium is occupied by the gullet, the 

 nucleus and some endoplasm which is not in the main stream. 

 The effect of this difference seems to be one affecting velocity 

 only, slowing it down, for in the Chara cell the endoplasm meets 

 with much less friction when moving in contact with the vacuolar 

 wall than when moving in contact with the ectoplasm. Its ve- 

 locity is still further reduced by the large food vacuoles which 

 are almost always carried by the endoplasm, for these vacuoles 

 behave like solid bodies in the endoplasmic stream. During 

 streaming these vacuoles are often seen coming close to the lim- 

 iting ectoplasm, when they act as obstructions to the flow of the 

 endoplasm. The velocity of the endoplasmic stream in para- 

 mecium is relatively slow, ten to twenty minutes being required 

 for a complete revolution. 



In Frontonia leucas, another large ciliate, rotational streaming 

 is under the control of the organism, and special use is made of it 



