Chapter II 

 HISTORICAL AND CRITICAL CONSIDERATIONS 



2. The Neogenetic and the Pamneristic Conceptions of 



Cell-Division 



Only a few decades back it was generally believed 

 that individual organs, such as the nucleus and the chlo- 

 rophyll grains, could always, or at least very frequently 

 originate from the undifferentiated protoplasm through 

 differentiation. However, in recent years, investigations 

 have not confirmed this neogenesis in a single instance. 

 Wherever the origin of an organ has been thoroughly 

 and comprehensively studied, with the present means of 

 investigation, the organ has been shown to originate 

 by a division of differentiated members already present. 



The organization of the protoplasts is not periodical, 

 nor evident only in grown cells. It is permanent, inher- 

 ent in all cells, and in all stages of their development. 

 The assumption of formation de novo gives place every- 

 w^here to the recognition of divisions : the neogenetic con- 

 ception gives way to the panmeristic* 



It is of interest to glance over the course of develop- 

 ment of our knowledge. In his "Lehre von der Pflan- 

 zenzelle," Hofmeister describes the nuclei according to 

 the knowledge of that time. They appear in the proto- 

 plasm as drops or masses of a transparent homogenous 

 substance, either in cells with few nuclei, of a definite 



*The view that all the organs of protoplasts, as a rule, multiply 

 only by division I call pamneristic. This assumption was maintained 

 for plant-cells for the first time in my plasmolytic studies. Cf. Vries, 

 H. de. Jahrb. Wiss. BoL 16: 489. 1885. 



