138 Historical and Critical Considerations 



plasm, no particular devices have been observed for as- 

 suring the possession of one or more nuclei at the cell- 

 divisions of each daughter-cell. Moreover they do not 

 seem necessary, owing to the great number and regular 

 distribution of the nuclei. Nuclear spindle and nuclear 

 barrel have therefore lost their significance in this case, 

 and accordingly they are probably not present, at least 

 not as a rule. Cell-division is essentially performed by 

 the plasmatic membrane and the granular plasm only. 



For the correct understanding of the processes of 

 normal cell-division, one law, which has been ascertained 

 by experiments on artificial division of living protoplasts 

 in former and more recent times, is of extreme import- 

 ance. I do not mean the adaptive processes of regener- 

 ation after wounding (these will be discussed in the 

 next paragraph), but the constriction of the uninjured 

 cell-contents in entire cells, and the division of the pro- 

 toplasts into two or more pieces during plasmolysis. The 

 respective cases I have put together in my ''Plasmoly- 

 tische Studien iiber die Wand der Vacuolen/'^^ They 

 teach that, in artificial constrictions of a protoplast, the 

 limiting membrane, the wall of the vacuole, and the gran- 

 ular plasm close their edges, apparently without any dif- 

 ficulty, and round off to form a new unit. In plasmolytic 

 experiments this is easily verified. Here one sees also, 

 how upon the restoration of turgor, the parts flow to- 

 gether again, their members uniting with the correspond- 

 ing organs of the other parts of the same protoplast. 



This power of combining with homologous parts 

 seems to be universally inherent in the three mentioned 

 organs of the plant-protoplast. The walls of the vacu- 

 oles show it wherever the numerous vesicles of cell-sap 



^^Jahrb. Wiss. Bot. 16: 501-505. 1885. 



