Cell-Division According to Mohl's Type 137 



unites with the latter, and is now gradually flattened by 

 it, and finally constricted. 



According to the principles of the theory of the vacu- 

 oles ascertained by Went and myself, it is probable that 

 the space containing osmotic substance and surrounded 

 by the connecting cylinder is a vacuole, which, contrary 

 to Strasburger's conception, 19 must have penetrated from 

 the outside between the two younger nuclei. It is just as 

 evident that this vacuole must be surrounded by a wall 

 of its own, and that this also forms the inner layer of the 

 connecting cylinder. The latter is also separated from 

 the other vacuoles of the cell-space, by a wall, and between 

 the two walls there lies, at least in the beginning, granu- 

 lar plasm. The changes of that vacuole which forms the 

 interior of the barrel during the whole process require, 

 of course, special investigation, made on living material. 20 



But there can be no doubt about the correctness of 

 Strasburger's conception, where he places the whole pro- 

 cess of cell-division, with the one exception of the divi- 

 sion of the nucleus, in the protoplasm itself. The daugh- 

 ter-nuclei are passive in this, the cytoplasm alone is the 

 active element. 



The chlorophyll-bands, the vacuole, and the granular 

 plasm are simply constricted by the plasmatic membrane 

 growing into the interior. The membrane itself finally 

 separates in the same manner, after having entirely closed 

 up the space remaining in the middle of the ring. 



In those poly-nucleate algae, the nuclei of which are 

 evenly distributed over the entire lining layer of proto- 



l9 Loc. dt. p. 17. 



20 Zacharias, in his discussion of Strasburger's work (Bot. Zeit. 

 46: 449. 1888), emphasizes also "that, on the living object, things may 

 exist which can be better recognized and interpreted there than by 

 fixing and staining." 



