HISTORICAL 3 



With regard to the importance of the movements of the protoplasm 

 in closed cells, various contradictory opinions have been expressed. Velten l 

 held that rotation was a very common phenomenon, and was exhibited by 

 the protoplasm of all cells at some stage or other of their life-history. It 

 does not, however, follow that the power of movement must always take 

 this particular form, or be immediately perceptible. Slow movements and 

 changes of form of the protoplast and its organs seem, however, to be possible 

 in all cases where no insurmountable physical obstacles are interposed. 

 De Vries 2 considered that streaming movements were of primary import- 

 ance for the transport of food-materials and even of water, and held that so 

 long as any cell could generate energy its protoplasm was in active move- 

 ment. This one-sided view was supported by Janse 3 , who observed that 

 in Caulerpa prolifera currents flow to and from the growing apices, and 

 that after wounding they usually make a detour to reach their original 

 destination, which otherwise dies. In those cases where no streaming could 

 be detected, de Vries supposed either that it was too slow to be visible, 

 or that the act of preparation had caused it to cease. Frank 4 showed, 

 however, that in most cases there is no active movement, but that an 

 external influence (section-cutting, change of temperature, &c.) can bring 

 streaming into play, and that this may cease again after a time, or may 

 persist during the remainder of the cell's existence. A particular stimulus 

 is not always effective. Thus Moore 5 found that leaves of Elodea might 

 be sectionized without streaming ensuing, and indeed no stimulus can 

 induce streaming unless the protoplasm has an inherent tendency to that 

 form of activity, and unless the necessary physical conditions are fulfilled. 



Ida A. Keller 6 stated that streaming was in most cases not a normal 

 phenomenon in the life of the cell, but was induced by injury or external 

 stimulation, and that whenever normal streaming was present in a cell 

 external stimuli simply increased its rapidity and intensity. Neither of 

 these statements, however, applies to all cases, and the exceptions to the 

 latter one are especially numerous. Wigand 7 supposed that long resting- 

 periods alternated with short periods of active rotation, and concluded that 

 streaming was awakened in cells under observation not so much by the 

 mechanical influence of preparation, as by the reflected light and heat rays 

 to which the preparation is subjected on the microscope-stage. Haupt- 

 fleisch 8 , however, has shown that a mechanical stimulus alone is sufficient to 



Bot. Zeitg., 1872, p. 147 ; Flora, 1873, P- 82. 

 Ueber die Bedeutung, &c., Bot. Zeitg., 1885, Nos. i and 2, p. i. 

 Jahrb. f. wiss. Bot., 1890, Bd. XXI, p. 163. 

 Pringsh. Jahrb., 1872, VIII, p. 220. 

 Journ. Linn. Soc., 1888, Vol. XXIV, p. 240. 

 Ueber Protoplasm astromung im Pflanzenreich, 1890, pp. 12, 40. 

 Botanische Hefte, 1885, I, p. 214; cf. also Hanstein, Das Protoplasma, 1880, p. 169. 

 Pringsh. Jahrb. f. wiss. Bot., 1892, Bd. XXI v. 



B 2 



