I02 



LECTURE VII. 



processes during the cell-formation of plants and animals are in all essential 



points alike. 



The following description is taken chiefly from the statements of Strasburger, 

 with which my own observations agree, at least in the points which appear important 

 to me : the questions still under discussion between the specialists in this province 

 may here be avoided as much as possible. 



The first preparations for the division of a vegetable cell are noticeable in the 

 changes of the cell-nucleus; and it is in fact in the visible elements of the nuclein 

 that the first indications and further course of the division of the nucleus are to be 



traced. 



'In general,' says Strasburger, 'the contents of the nucleus (the nuclein) become 

 coarsely granular : hereupon the granules fuse with one another into shorter or longer 



FIG. 104.— Changes in the cell-nucleus during the division of the mother cell of a stoma 

 of Iris ptimtla (ij. In 9 the division is completed and the two guard cells have been 

 produced. The dark portions are nuclein (X 8S0— after Strasburger), 



filaments, curved in all directions. The nucleoli often remain preserved in vegetable 

 cells for a long time, much longer than in animal cells : finally they too enter into the 

 formation of filaments; and the wall of the nucleus also becomes concerned in the 

 process. In the rare cases where this does not happen, they disappear, at least at 

 the poles of the nucleus. When the wall of the nucleus has become, as is usual, 

 completely absorbed, the filaments lie immediately in the surrounding protoplasm of 

 the cell, and may in many cases be dispersed somewhat widely in it. The nuclear 

 filaments (filiform arrangement of the nuclein) are, particularly in round cell-nuclei, 

 nearly equally distributed through the entire space of the nucleus ; in elongated cell- 

 nuclei they follow more or less the longitudinal axis. They begin later in all cases to 

 place themselves parallel to one another. If an elongation of the cell-nucleus in a 

 definite direction has taken place meanwhile, the filaments become elongated in the 

 same direction. Two poles become plainly distinguishable in the cell-nucleus. The 



Kenntniss der ZelU undihrer Lebenserscheinungen,' I. and II ; in Archiv fiir mikroskopische Ana- 

 tomie, Bonn, Bd. XVIII. and XX. 1 880-81 ; and Schmitz, ' Struktur des Protoplasmas und der 

 Zellkerne! in Sitzungsber. der niederrhein. Ges. fiir Nat. und Heilk. zu Bonn, 13 July, 1880. 



