PROTOPLASMIC STREAMING 285 



streaming is not shown by the cells of the primary meristem, irregular 

 sliding movements appearing as the cells enlarge and vacuoles begin to 

 appear, and circulatory streaming being then established, which passes 

 into rotation if the protoplasm is restricted to the peripheral membrane. 

 The streaming, after attaining a maximum at a certain period of development, 

 then often persists until death 1 , and in the case of Chara and Nitella 

 cannot be stopped for any length of time without killing the cells. In 

 the cells of Elodea and Vallisneria the newly-awakened streaming may 

 die away again, and it is even possible by prolonged culture in strong 

 sugar-solution to render the protoplasm of Elodea permanently immotile 2 . 

 That streaming is possible in the absence of well-defined vacuoles is shown 

 by the plasmodia of Myxomycetes, although here the streaming is pre- 

 sumably the direct result of the amoeboid expansion and contraction of 

 the peripheral layers. The non-vacuolated protoplasm of certain cells of 

 the primary meristem may also show slight sliding movements under special 

 conditions 3 , and the existence of streaming in the threads crossing the cells 

 of Spirogyra shows that well-defined streaming may be shown by embryonic 

 cells containing a large vacuole. 



Although distinct streaming movement does not appear to be a general 

 necessity of protoplasmic existence, there can be no doubt that it has in 

 most cases a definite purpose. Usually it appears to have as its function 

 the rapid transport of material from one part to another, and it is largely 

 for this reason that it only appears when the developing cells reach a certain 

 size, and becomes inextricably connected with vitality in the extremely 

 large internodal cells of Chara and Nitella. In the latter the protoplasm 

 is able to stream several times around the cell in the time required by 

 most dissolved substances for complete diffusion across its length, whereas 

 in small cells diffusion is more rapid than streaming 4 . The absence of 

 streaming from very small cells is, however, also partly due to the relatively 

 high internal resistance to flow 5 . It is, in any case, always possible that the 

 streaming movement may be an accessory but unavoidable accompaniment 

 of some other form of vital activity. A certain advantage is probably 

 gained' by the absence of streaming from the meristem cells in so far as 

 the grouping and arrangements preceding cell-division are undisturbed. 

 Cell-division in Amoeba and Spirogyra and nuclear division in Myxomycetes 



1 Cf. Wigand, Bot. Hefte, 1885, Heft i, p. 186 ; also Nageli, Beitrage z. wiss. Bot., 1860, Heft ii, 

 p. 61 seq. ; Vesque-Piittlingen, Bot. Ztg., 1876, p. 574; Braun, Ber. iiber die Verhandl. der Berl. 

 Akad., 1852, p. 214. 



2 Ewart, Protoplasmic Streaming in Plants, 1903, pp. 15, 58. 



* Cf. Biitschli, Archiv f. Entwickelungsmechanik, 1900, Bd. x, p. 52. 



4 This is owing to the fact that the time required for complete diffusion is proportional to the 

 square of the distance across which diffusion occurs. Cf. Ewart, On the Ascent of Water in Trees, 

 Phil. Trans., 1905, p. 40 (reprint). 



5 Ewart, Protoplasmic Streaming in Plants, 1903, pp. 26-30. 



