﻿3i6 BOTANICAL GAZETTE [may 



As the highly complex nature of the typical nucleus has 

 doubtless been the result of the demand for a physiological 

 division of labor in the cell, there is no reason why we should^ 

 expect to find such a condition in the primitive cell of the 

 Cyanophyceae or Bacteria. The majority of the writers who have 

 investigated the c^'tology of these forms agree that chromatin- 

 like granules exist in these primitive cells, but that these granules 

 are surrounded by neither nuclear sap nor membrane, and many 

 therefore do not regard these granules as representing the nu- 

 cleus. As I have attempted to show that the so-called nuclear 

 membrane is merely the inner limiting membrane of cytoplasm, 

 and that every typical cell passes through a phase in its history 

 when it consists of nothing but chromatin granules, the writer 

 sees in this a possible reconciliation for the divergence of opinion 

 that is held in regard to the nucleus of the Cyanophyceae. For 

 might we not regard that stage of the daughter nucleus when it 

 is devoid of a membrane as representing a phase in its ontogeny 

 which approaches that primitive condition which we find in the 

 cells of the bacteria and Cyanophyceae, although the chromatin- 

 like bodies in the cells of these forms may not be the ancestral 



nucleus. 



In conclusion, I take pleasure in acknowledging my indebt- 

 edness to Dr. Bradley M. Davis and Dr. Charles J. Chamberhn 

 for advice, and to the Botanical Department of the University of 

 Chicago for the excellent facilities for cytological research 

 which were placed at my disposal. 



SUMMARY. 



The results of the above observations may be briefly summa- 

 rized as follows; 



The typical nucleus of the higher plants is a water cavity 

 structurally similar to that of the cell vacuole. 



The chromatin is the only permanent constituent of the 

 nucleus. The karyolymph, linin, nucleoli, and membrane are 

 renewed with each succeeding mitosis. 



The nuclear membrane originates like the tonoplast. It 

 is formed by the cytoplasm coming in contact with the karyo- 



