AMEBOID MOVEMENT 95 



tinned presumably as long as the myxomycete is in the plasmodial 

 stage. With every change in the direction of movement of stream- 

 ing, there is produced, however, a change in the shapes of the 

 pseudopods, so that with a number of oscillations in streaming 

 an appreciable degree of locomotion is effected. The direction of 

 locomotion can be markedly affected by changes in light intensity 

 and moisture distribution, as shown by the observations of Bar- 

 anetzsky ('76), Stahl ('84) and others, but just how these changes 

 in the direction of locomotion were produced is not recorded. 

 There is a definite ectoplasm and a definite endoplasm in the 

 myxomycete plasmodia, but the details of their transformations, 

 the one into the other, have not been determined; but since the 

 surface layer is stationary, it is probable that there is no such 

 regular transformation of endoplasm into ectoplasm at the an- 

 terior ends of pseudopods as there is in ameba. But this phase 

 of the subject needs further investigation before any conclusions 

 can be drawn. The power of contractility is present, but appar- 

 ently only to a slight degree. Too little is known of the stream- 

 ing process in these organisms to compare it in detail with the 

 same phenomenon in rhizopods. 



The streaming of protoplasm in plants has received a good 

 deal of attention, though only comparatively little experimental 

 work has been done. Streaming is observed in a great many 

 plant cells, and in some cells such as the large internodal cells of 

 Chora and Nitella, the process may be easily observed. The es- 

 sential features of a plant cell in which streaming occurs are, first, 

 the external cell wall of cellulose, which of course prevents any 

 change of shape in the cell such as is observed in naked proto- 

 plasts as, for example, ameba. Inside of the cell wall is a layer 

 of ectoplasm which has essentially the same properties as the ecto- 

 plasm of amebas. In some cells such as those of Chara, the ecto- 

 plasmic layer is thick and contains nearly all the chloroplastids, 

 while in the leaf cells of Elodea the ectoplasm is extremely thin 

 and is practically free from chloroplastids. In the interior of 

 the cell are found the streaming endoplasm and one or more large 

 vacuoles filled with cell sap. 



The streaming is of two types which are often distinguished 

 from each other by the names rotational and circulatory. But the 



