RELATION BETWEEN CELLULAR AND NUCLEAR DIVISION 41 



of oxygen, and also treatment with chloroform or ammonia, cause cell-division 

 and the formation of a cell-plate to be suppressed although the division of the 

 nucleus may continue. A similar result was observed by Wildemann in Desmids 

 at low temperatures, by Gerasimoff in Spirogyra^ and by Klebahn in the filaments 

 of an Oedogonium attacked by a fungus (Lagenidium) \ Nor is it surprising 

 that in Gerasimoff's observations on Spirogyra cell-division commenced, but not 

 nuclear division. 



Although we cannot precisely determine the different factors involved, 

 there is no doubt that cell-division is a physiological process, and is not the 

 direct result of the same surface-tension forces that produce the segmenta- 

 tion of a free fluid thread into a series of spherical drops 2 . Cell-division, 

 with the nuclear and cytoplasmic movements it involves, may in fact occur 

 in spherical cells, but it is suppressed in the long thin tubular cells of 

 Vaucheria, and of laticiferous systems. In these latter cases the internal 

 osmotic pressure keeps the protoplasmic lining tightly pressed against the 

 cell-wall, and hence renders it impossible for the surface-tension action in 

 question to come into play. In plasmolysed protoplasts, however, such 

 segmentation often occurs, but although physical laws act inside the 

 protoplast as well as outside it, it must be remembered that the protoplasm 

 is by no means a homogeneous fluid, and that its surface tension as well as 

 the cohesion of its parts may undergo local alteration as the direct result of 

 its physiological activity. 



The partition-walls in a cellular tissue do approximately correspond in 

 position to the flattened dividing films in a mass of soap-bubbles of equal 

 size, but it is an open question whether the surface-tension-forces exercise 

 a directive action upon the physiological processes involved in cell-division. 

 No safe conclusions can be drawn from the similarity of the final result in 

 the two cases, for the living organism often produces purposeful shapes and 

 arrangements which superficially seem to obey a definite physical law. 



The similarity between the arrangement 'of the partition-walls in a dividing 

 tissue with that in a froth of soap-bubbles was first pointed out by Berthold 3 . 



T. xni). Demoor supposes that the nuclei may divide independently after the death of the 

 cytoplasm, and in the absence of oxygen. These results, however, are not altogether satisfactory. 

 Cf. Samassa, Ueber d. Einwirkung von Gasen auf d. Plasmastromung, 1898, p. 6. 



1 De Wildemann, quoted by Demoor, I.e., p. 82; Gerasimoff, Ueber kernlose Zellen der 

 Conjugaten, 1892 (repr. from Bull. d. 1. Soc. d. Nat. d. Moscou) ; Ueber ein Verfahren, kernlose 

 Zellen zu erhalten, 1896, ibid. ; Klebahn, Jahrb. f. wiss. Bot., 1892, pp. 24, 263. Further details by 

 Hertwig, 1. c. ; Zimmermann, 1. c. 



2 Cf. Berthold, Protoplasmamechanik, 1886, p. 87. No such breaking-up occurs in the 

 elongated chlorophyll bands of Spirogyra. Cf. Berthold, I.e., p. 170. It is not known why the 

 plasmodium of a Myxomycete, when imbedded in gelatine, breaks up into pieces in a manner 

 resembling the free-cell formation in a zoosporangium of Saprolegnia. Cf. Pfeffer, Zur Kenntniss 

 d. Plasmahaut u. d. Vacuolen, 1890, p. 277, footnote; Demoor. I.e., p. 244. 



3 Berthold, Protoplasmamechanik, 1886, p. 220; Errera, Ber. d. Bot. Ges., 1886, p. 441 ; Bot. 

 Centralbl., 1888, Bd. xxxiv, p. 395; de Wildemann, L'attache d. cloisons cellulaires, 1893. In 



