Autonomy of the Limiting Membrane 163 



I agree here with Zacharias 72 who, from observation on 

 Chara, is of the opinion that the cell-plate elements origi- 

 nate from the cytoplasm surrounding the nuclear figure. 

 I wish also to recall here an opinion of Flemming's, ac- 

 cording to which, cell-division in plants and animals 

 generally begins with a constriction of the protoplast. 

 This constriction has not been observed in many prepa- 

 rations for the only reason that it is frequently unilateral, 

 and therefore requires a special position of the cell under 

 the microscope in order to be seen. 78 



Platner's view that the spindle fibers are currents of 

 the granular plasm requires further investigation. For 

 this purpose direct observation on the living object is 

 necessary. Obviously the plasma-currents have, until 

 now, been sadly neglected in the study of cell-division. 



There are still left for us to consider the instances of 

 so-called free cell-formation, which probably represent 

 the most striking exceptions to the rule of the autonomous 

 origination of the plasmatic membrane. By free cell- 

 formation is meant those cases in which not all of the 

 protoplast of the mother-cell is used in the formation of 

 the daughter-cells. 74 The new cells were thought to have 

 originated in the interior of the mother-cell, and there- 

 fore without any contact with the limiting membrane. 



72 Zacharias, E. Ueber Strasburger's Schrift Kern-und Zell- 

 theilung im Pflanzenreiche. Jena. 1888. Bot. Zei't. 46: 456. 1888. 



73 Flemming. Zellsubstanz, Kern-und Zelltheilung. p. 243. 

 1882. 



74 In the most recent interview of the pertinent literature, Zim- 

 mermann suggests that the name free cell-formation be not used for 

 these phenomena, but for the formation of free cells, i. e., of such that 

 lose their connection with the mother-cell. If it should be discovered 

 that a free cell-formation in the old sense, does not exist in the plant- 

 world, this suggestion would certainly be acceptable. Cf. Die Morph- 

 ologie und Physiologie dcr Pfianzenzclle, p. 160. 1887. 



