Origin of Sexuality 259 



plemental sex-cells, when these are ripe for conjugation. But 

 in order to grasp the significance and connection of this it 

 will now be necessary to review shortly the entire question 

 of cell di\dsion as witnessed in nucleated plants. 



In the preceding context we have developed the view that 

 the nucleated cell consists of two main hereditary factors, 

 the protoplasm that is associated with biotic energy, and the 

 chromatin that is associated with cognitic energy. 



The chromatin is, in most cases, centered in the nucleolus, 

 and from the latter threads radiate out into an area of the 

 cell substance that forms a chromatin "sphere of influence," 

 which we have commonly called the nucleus. These threads 

 again fuse in part to form the nuclear membrane, while through 

 this, and in part also from its surface, chromatin threads radi- 

 ate out into the protoplasm, and in some cases at least — prob- 

 ably always in surface cells — end in many fine processes in 

 the ectoplasm, though in tissue cells they seem to form inter- 

 cellular connecting threads through pores in the common 

 walls. 



The above view, first reached by the writer in ISS'^, from 

 study of dividing plant and animal cells, was again shortly 

 set forth in his paper on hybrid structure in 1 89*^2 (63). In 

 recent years the valuable and original studies of Hartog on 

 "dual forces of the dividing cell" have shed confirmatory light 

 on it, as the subjoined pages will bring out. 



Of all ordinary tissue cells known to the writer none in his 

 estimation approaches Spirogyra as yielding a vivid picture 

 stage by stage of cell division, that, in the act, gives a key to 

 other and more complicated types in the higher plants and 

 animals. S. nitida and *S. maxima are the most convenient, 

 and the former is a widely distributed type, for study. 



When cell-division commences the nucleolar substance first 

 becomes the center of energizing changes that result in sub- 

 division of its substance into many smaller masses or chro- 

 mosomes, as set forth by Mitzkemtsch (102: 85). Though 

 too minute for detailed study hitherto, these bodies e\ddently 

 correspond to the chromosomes of liigher cells, and in breaking 

 u]) into definite masses we doubtless have a halving or segre- 

 gation of the constituent chromatin materials that are to confer 

 definite characters on the daughter cells. When this has been 



