THE GROWTH OF THE CELL 271 



has also been thrown on Wasiliewski's work by the expernnents of Nemec 

 (1904, Jahrb. f. wiss. Bot. 39, 645). At present it cannot be affirmed with 

 certainty whether * amitosis ' does take place under the conditions mentioned 

 above; still less certain are we of the results contingent on it.] The daughter- 

 cells, which are produced in this way, behave normally and divide mitotically 

 later on. 



Cell division also occurs without any visible bi-partition of the nucleus. 

 This is the case, for instance, in the multi-nucleate cells of Cladophora ; division 

 takes place as in the case of Spirogyra, but the partition wall is not formed on 

 a nuclear spindle. The cells of Cyanophyceae and Bacteria also exhibit normal 

 division, yet they appear generally to contain no nuclei. Further, Geras- 

 siMOFF (1899) succeeded in so altering the division process in Spirogyra that one 

 of the daughter-cells contained two nuclei, the other none ; and although in this 

 case also the transverse wall could not be formed on the spindle still it showed 

 no difference in appearance to the normal wall. Gerassimoff (1901) also suc- 

 ceeded in some experiments in so influencing the cells during division that the 

 division of the nucleus was suppressed while cell division still went on ; one 

 daughter-cell thus had one nucleus while the other had none. The cell contain- 

 ing the nucleus and its descendants were distinguished for a long time by their 

 remarkable size, and attained a great length before proceeding to divide afresh. 

 The nucleus has also a certain influence on the specific amount of division, 

 which depends also on many internal and external factors. We cannot go 

 into these here and will content ourselves with noting that one internal factor, 

 viz. the function of the cell, influences in a remarkable way the amount of division 

 it undergoes. The varied size of different cells in the complex plant depends 

 on this fact ; but the same phenomenon may be observed in quite simple 

 organisms also. Compare, for example, the difference in size between the 

 ordinary vegetative cells and the sexual (male) cells in Oedogonium. In spite 

 of its variability the amount of division in cells is in general a character of 

 the species. Thus cells as small as those which occur in Bacteria are unknown 

 in Phanerogams ; cells as large as those of Caulerpa, are found in flowering 

 plants only in isolated positions and adapted to carrying out special functions 

 (laticiferous tubes). 



When a cell has reached a certain size it divides, and so attains once more 

 its normal size, and division into two as a rule leads to this result. Often, how- 

 ever, a formation of many cells takes place, four or even more cells being formed 

 from one. To give illustrations of this phenomenon and to describe the arrange- 

 ment of the walls in such cases would lead us too far, and so we may merely 

 refer to detailed descriptions of cell morphology. 



Although in general a certain amount of growth precedes cell division still 

 this is not a universal condition of that division. Certain embryonic cells divide 

 into numerous small cells without exhibiting any actual growth ; thus the ovum 

 of Fucus, the spores of many Hepaticae and Fungi, the segments of the apical 

 cell of Stypocaulon are illustrations in point, but of these we shall speak in our 

 next lecture. 



Bibliography to Lecture XXI. 



Ber. d. bot. Gesell. 8, 61. 



Studien iiber Protoplasmamechanik. Leipzig. 

 Bihang svenska Vet. Akad. Handl. 23. 

 Einfl. d. Temperatur und des Lichtes auf den Turgor. Diss. 



Flora, yz, 298. 



Jahrb. f. wiss. Bot. 23, 254. 



Ibid., 26, 587. 



Bot. Ztg. 56, II. Abt. Sp. 221. 



