/ 



I 



1917] DUNN—DUMONTIA 453 



mitosis, since they are considerably larger and divide more actively 

 than the vegetative nuclei. The cell history of these branches is 

 also of some aid in identifying stages in nuclear division. All the 

 chromatin in the nuclei of most of the young carpogonial branches 

 is in the nucleolus (figs. 22-30). This is true of the nuclei also in 

 cells 4, 5, and 6 of the mature branches (figs. 32-34, 37). The 

 nuclei in cells 1,2, and 3 of the mature carpogonial branches have 

 a tendency to divide. The failure to secure any stages of mitosis 

 in the nuclei of the cells of the young carpogonial branches is 

 probably due to the fact that these cells divide very rapidly. The 

 chromatin in the nuclei in most of the uninucleate cells of the mature 

 auxiliary cell branches is not in the nucleolus but in a number of 

 small granules (figs. 48, 51-55)- The nuclei in the cells of these 

 branches divide often (figs. 46, 48-50). The frequency of division 

 of these nuclei is probably due, as in the basal cells of the carpo- 

 gonial branch, to the fact that these cells are usually completely 



Thus in the resting nuclei 



asm 



of the cells of the carpogonial branches, as in the tetraspores and 



chromatin 



The following changes are observed in the nuclei in prepara- 

 tion for division. Radial fibrillae appear running from the nucleolus . 

 to the nuclear membrane (cell 2, fig. 55) . Small chromatin granules 

 pass out from the nucleolus, along the fibrillae, to the nuclear 



■ 



membrane. When the granules first appear on the linin strands, 

 there is no appreciable decrease in the size of the nucleolus. The 

 position of these granules when they first appear indicates that 

 they have come from the nucleolus. Of the 6 granules present 

 in fig. 77, 3 are in contact with the nucleolus, and only i has yet 

 reached the periphery of the nucleolus. Nearly all of the granules 

 at a slightly later stage are present only at the points where the 

 fibrillae terminate in the nuclear membrane (fig. 78). More linin 

 strands are formed which connect the radial fibrillae already 

 present (fig. 79). All of the chromatin evidently passes out of 



becomes 



a thp linin net. The 



net disappears just before the nucleus divides (fig. 80). Practically 

 all of the chromatin in the nuclei which have just divided is in 7 

 fairly uniform granules (cell 4, fig. 52). The nucleus of cell 4, 



