GENERAL 263 



Various internal amoeboid movements are still possible, as well as streaming, 

 and slow changes in the shape and position of the organs. Visible move- 

 ments are never entirely absent, though often extremely slow, so that 

 a slight change of position can be seen only after a considerable time. 

 Slow movements necessarily accompany the growth of the cell and the 

 conversion of a solid protoplast into a vacuolated one, while cellular and 

 nuclear division involve special grouping and separating movements. Active 

 growth does not, however, involve active movement, and protoplasmic stream- 

 ing is, for instance, absent from the cells of the primary meristem. Streaming 

 persists in many adult cells so long as they remain living, whereas in other 

 cells it is not aroused during the most active respiration and metabolism. 



The ejection of seeds may be regarded as a passive movement even 

 when due to tensions created by vital activity. The same applies to the 

 rise of algal filaments owing to the adherence of bubbles of gas to them. 

 If the gas is oxygen produced by photosynthesis, the movement is 

 indirectly due to vital activity, just as when the air-spaces formed in shoots 

 cause them to ascend as soon as they have developed from the resting buds, 

 which sank the previous autumn owing to their higher specific gravity 1 . 

 Certain lower organisms possess gas vacuoles within the protoplasm, and 

 these may be used like the air-bladders of fishes to produce ascent and 

 descent in the water 2 . It it, however, uncertain to what extent modifica- 

 tions in the specific gravity of the protoplasm and cell-sap may take part 

 in flotation 3 . 



For such movements not only the specific gravity but also the shape 

 and relative amount of surface are of importance. This is evidenced by 

 hairy and winged seeds, and by the transport of dried bacteria and other 

 micro-organisms, as dust particles in the air 4 . In the same way slow 

 currents of water suffice to prevent the settling of minute particles denser 

 than the water, although in the case of plankton organisms active move- 

 ments may aid in producing the same result 5 . 



1 Cf. Goebel, Pflanzenbiol. Schilderungen, 1893, T. ii, p. 356. On the work done in forming 

 intercellular spaces cf. Pfeffer, Energetik, 1892, p. 232. 



a On gas vacuoles see Engelmann, Pfliiger's Archiv f. Physiol., 1869, Bd. n, p. 307 ; Klebahn, 

 Flora, 1895, p. 241; Strodtmann, Biol. Centralbl., 1895, Bd. xv, p. 113; Celakovsky, Ueber den 

 Einfluss des Sauerstoffmangels auf die Bewegung einiger aeroben Organismen, 1898, p. 21 (reprint 

 from Bull. Internationale de 1'Academie de Bpheme) ; Wille, Biol. Centralbl., 1902, Bd. xxii, 

 pp. 207, 357 ; Molisch, Bot. Ztg., 1903, p. 47 ; Hinze, Ber. d. bot. Ges., 1903, p. 394. 



3 Cf. Brandt, Biol. Centralbl., 1895, Bd. xv, p. 855 ; Schiitt, Jahrb. f. wiss. Bot., 1899, 

 Bd. xxxm, p. 680. 



4 Nageli, Sitzungsb. d. Bayerisch. Akademie, 1879, p. 389; Ostwald, Biol. Centralbl., 1902, 

 Bd. XXII, p. 596. 



5 On Brownian or 'molecular' movements see Exner, Ann. d. Physik, 1901, n, 4, p. 843; 

 Lehmann, Molekularphysik, 1889, Bd. I, p. 264; Bd. u, p. 7. Seeds and spores which are not 

 wetted by water may be supported on the surface-tension film, and appear to float. Cf. Nageli, 

 Beitrage z. wiss. Bot., 1860, Heft ii, p. 105; Nageli u. Schwendener, Mikroskop, 1877, 2. Anfl., 

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