Autonomy of the Limiting Membrane 163 



I agree here with Zacharias^^ who, from observation on 

 Char a, 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.^^ 



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.^* 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. 



'^Zacharias, E. Ueber Strasbnrger's Schrift Kern-und Zell- 

 theilung im Pflanzenreiche. Jena. 1888. Bot. Zcit. 46: 456. 1888. 



^^Flemming. Zellsuhstans, Kern-und ZeUtheilung. p. 243. 

 1882. 



^^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 Pflanzenzelle, p. 160. 1887. 



