336 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



vented. When growth took place the removal of the reserve-materials 

 allowed more rapid readjustment to occur. 



Dehnecke l found that chloroplastids containing starch when kept 

 in movement by long-continued rotation on a klinostat ultimately expelled 

 the contained starch-grains and became more or less deformed, but the 

 exact origin of this effect is uncertain. The displacements produced by 

 high centrifugal action cannot be supported indefinitely, and Andrews 2 

 found that a disturbance of growth was produced even by short exposure. 



It is evident from these experiments that the nucleus, and also the 

 cytoplasm, have a higher density than the cell-sap, while the nucleolus and 

 chromatin have a higher density than the rest of the nucleus. The latter 

 may, in some cases, be driven out of the nucleus by very high centrifugal 

 forces 3 . According to Nemec 4 , the nuclei in the cells of the root-cap move 

 upwards when the root is inverted. Since this movement is in the opposite 

 direction to that expected from their density, we must at present ascribe 

 a geotactic irritability to the nucleus, although the phenomenon may result 

 merely from the downward movement of the starch-grains. 



Starchless chloroplastids, and all chromatophores excepting those in 

 the petals of Caltha pahtstris 5 , are denser than the cell-sap. The centri- 

 fugal movement of the oil-bodies of Hepaticae show that they do not 

 consist solely of oil, which, being less dense, moves centripetally 6 . Latex 

 may be separated by centrifugal action in the same way as milk 7 . It 

 has not yet been determined whether a permanent displacement can be 

 produced without the plant being killed. Mottier was, however, able 

 to produce unequal cell-division as the result of the accumulation of the 

 protoplasm on one side 8 , while Miehe 9 was successful in reversing the 

 polarity of the initial cell of a stoma by centrifugal action. 



SECTION 72. Geotactic Reactions. 



According to Schwarz 10 , Englena viridis and Chlamydomonas pulvis- 

 cuhis are negatively geotactic, and the same applies, according to Aderhold, 

 to Haematococcus lacustris, and in a less degree to the zoospores of 

 Ulothrix tennis. The experiments were performed in darkness, and partly 



I Dehnecke, Ueber nicht assim. Chlorophyllkorper, 1880, p. u. 2 Andrews, 1. c., p. 21. 

 3 Andrews, 1. c., p. 36 ; Mottier, 1. c., p. 352. 



* N6mec, Ber. d. hot. Ges., 1902, p. 344. Cf. Andrews, 1. c., p. 35. 



6 Andrews, 1. c., p. 37. Andrews, 1. c., p. 34. 



7 Andrews, 1. c., p. 24. 8 Mottier, 1. c., pp. 331, 357. 



9 Miehe, Flora, 1901, p. 109. 



10 Fr. Schwarz, Ber. d. hot. Ges., 1884, p. 51. 



II Aderhold, Jenaische Zeitschrift f. Naturwiss., 1888, N. F., Bd. xv, p. 321 ; Massart, Bull. de 

 1'Acad. royale de Belgique, 1891, 3" ser., T. xxil, p. 164; Jansen, Bot. Centralbl., 1893, Bd. LVi, 

 p. 20. 



