No. 466.] STUDIES ON PLANT CELL. VIII. 725 



appearing as chromosomes during mitosis and the nucleoli. 

 These structures are so easily recognized and play such impor- 

 tant parts in the events of nuclear division that they command 

 attention at once as the essential elements in the nucleus. The 

 nucleus may also contain other material such as linin which, 

 however, does not seem to have a fixed form or behavior in the 

 cell. Finally there are certain kinoplasmic structures, as cen- 

 trosomes, centrospheres, and blepharoplasts, whose behavior 

 throughout cell history has been much discussed. We shall now 

 consider the most important of these structures, those which 

 seem essential to the cell in ontogeny. 



The outer plasma membrane naturally retains its morphologi- 

 cal entity throughout all cell divisions with such slight changes 

 as when new parts are intercalated into its area through the 

 vacuoles that are utilized in the segmentation of protoplasm. 

 Vacuolar membranes are constantly shifting and cannot be fol- 

 lowed during cell division excepting in such cells as have one 

 large central vacuole (the tonoplast of De Vries). Such a cen- 

 tral vacuole is much more characteristic of old cells and tissues 

 than of young or embryonic regions. There is certainly no 

 reason to suppose that it has organic existence through any very 

 extended period of the life history. The nuclear membrane 

 becomes lost during the prophase of mitosis and there is .much 

 evidence that its kinoplasm contributes in some cases to the 

 formation of spindle fibers. Thus the nuclear membrane disap- 

 pears as a structure in the cell during mitosis and new vacuoles 

 are formed around the assemblages of daughter chromosomes 

 during telophase, leading of course to the formation of fresh 

 nuclear membranes at their surface of contact with the sur- 

 rounding cytoplasm. 



There is perhaps no region of the cell protoplast that presents 

 such different appearances through long periods of the cell -his- 

 tory as the trophoplasm. This is largely due to the varying 

 character of the inclusions which are not in themselves proto- 

 plasmic but which give a mixed structure to the trophoplasmic 

 regions of the cell. The inclusions may be carbohydrate or pro- 

 teid bodies held within spaces in the trophoplasmic groundwork 

 or they may be globules of oil or fatty substances. These 



