3 02 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



character to that of a thread drawn from a viscous liquid. Any secretion 

 of mucilage in the interior of the protoplasm would also produce a certain 

 amount of displacement reversible by the reabsorption of the mucilage. 



Nuclear division may be accompanied or preceded by an increase in the total 

 amount of nuclear material, and may take place independently of the cytoplasm, 

 although in mitotic division nucleus and cytoplasm come into close relationship 

 during the process and the latter forms the threads of the ' nuclear ' spindle *. It 

 is, however, uncertain what part is played by the centrosomes, which are in fact absent 

 from most plant-cells 2 . The mechanics of amitotic, and still more of the remarkable 

 movements involved in mitotic, division are indeed quite unknown. It is, however, 

 certain that they may be produced in a variety of ways, so that experiments with 

 non-living materials do not afford definite evidence as to the nature of the physio- 

 logical processes involved. Butschli 3 was able to produce radiations resembling 

 those shown by dividing nuclei by the contraction of air-bubbles embedded in 

 solidifying gelatine and also in emulsions of oil and soap under special conditions 4 . 

 Fischer 5 produced remarkable radiations arranged around the remains of the nucleus 

 as a focus by precipitating albumose in dead cells of Elder-pith. In this case the 

 nucleus acts merely as a centre of deposition, so that in the living cell it may also 

 play a passive part in the production of the radiations formed around it. The 

 grouping of particles of iron in a magnetic field yields similar configurations 6 , but 

 the magnetic properties of the cell constituents are incapable unaided of directly 

 producing any such grouping in the strongest magnetic fields available 7 . No actual 

 facts are, however, known as to the mode of movement in any single phase of the 

 changes, and even if the motion of the chromosomes should prove to be due to the 

 tension or pressure exercised by the threads of the spindle 8 we have still to determine 

 the mode of action of these threads themselves. 



The external conditions may influence the character and progress of cellular and 



1 See R. Hertwig, p. 698; Strasburger, I.e., 1900, p. 118; Zimmermann, Morphologic u. 

 Physiol. d. pflanzlichen Zellkerns, 1896, p. 48. 



2 Cf. Strasburger, Histologische Beitrage, Heft vi, 1900, p. 156 ; Ber. d. bot. Ges., 1901, p. 458 ; 

 R. Hertwig, Abhandlg. d. Bayrisch. Akad. d. Wiss., 1898, Bd. xix, p. 690; Mottier, Fecundation in 

 Plants, 1904, p. 2. 



3 Butschli, Unters. iiber Structuren, 1898, p. 156. 



4 Butschli, Unters. ii. mikroskopische Schaume, 1892, pp. 29, 159, 166. Cf. also Strasburger, 

 Bot. Zeitung, Referate, 1900, p. 300; Zacharias, Ber. d. bot. Ges., 1902, p. 298. 



5 A. Fischer, Fixirung, Farbung u. Bau d. Protoplasmas, 1899, p. 206. 



6 Cf. Errera, Compt. rend, de la Soc. royale de botanique de Belgique, 1890, T. XXIX, p. 17 ; 

 Butschli, I.e., 1898, p. 169; Rhumbler, Archiv f. Entwickelungsmechanik, 1903, Bd. XVI, p. 476; 

 Seddig, Ann. d. Physik, 1903, Bd. u, p. 815. 



7 Ewart, Protoplasmic Streaming in Plants, 1903, p. 45. 



' The theories concerning cell-division are mainly based upon preconceived hypotheses, so that 

 nothing is to be gained by their discussion. Cf. Butschli, 1. c., 1892, p. 160 ; Ziegler, Verhandlg. d. 

 deutsch. zoologischen Ges., 1895, p. 62; R. Hertwig, Abhandlg. d. Bayr. Akad., 1898, p. 694; 

 Rhumbler, Archiv f. Entwickelungsmechanik, 1898, Bd. vil, p. 535; Ergebnisse d. Anatomie u. 

 Entwickelungsgeschichte, 1898, Bd. vni, p. 605; A. Fischer, I.e., pp. 224, 257; Bethe, Bot. 

 Centralbl., 1902, Ed. LXXXIX, p. 513; Hacker, Praxis u. Theorie d. Zellen- u. Befruchtungslehre, 

 1899, p. 73- 



