CELL-DIVISION. 33 



left, whose elements diverge, meeting the concave plasma membrane 

 at different points. Other delicate fibers extend from the spirem in 

 all directions towai-d the plasma membrane. As soon as the nuclear 

 membrane appears these radiating fibers become more uniformly dis- 

 tributed about the nucleus. They undoubtedly take part in the forma- 

 tion of the spindle in the division of the daughter nucleus. 



FREE CELL-FORMATION. 



The most beautiful and best known illustration of typical free cell- 

 formation is found in the development of the spores in the ascus of 

 certain Ascomycetes as described by Harper. 



The delimination of the spores from the cytoplasm in Erysiphe fol- 

 lows immediately after the close of the last of the three successive nuclear 

 divisions which furnish the eight nuclei for the spores. The entire 

 process is accomplished by those kinoplasmic fibers which constitute 

 the polar radiations of the last nuclear division and in a manner quite 

 peculiar to asci. 



All of the eight nuclei pass through the anaphase at the same time, 

 and, when in the resting condition, cannot be distinguished one from 

 the other, with the exception of those that lie close to the wall. The 

 polar radiations persist in connection with those nuclei that form 

 spores, while from those which do not the radiations disappear entirely. 

 The chromatin lies mostly free in the nuclear cavity, but it is always 

 in communication with the nuclear membrane, especially near the 

 centrosphere (Fig. 12, A). As the first indication of cell-formation, 

 the nucleus becomes pointed and develops a beak-like prolongation on 

 the side next to the pole or centrosphere. This point or beak gradually 

 elongates, so that the centrosphere becomes farther removed from the 

 body of the nucleus (Fig. 12, B). As soon as the beak reaches a 

 length which exceeds slightly the diameter of the nucleus, its growth 

 ceases. This beak consists not of a single fiber or thread but of a 

 slender cylindrical tube arising abruptly from a rather broad base. 

 Into the tube there extends quite to the centrosphere a continuation of 

 the chromatin net, by which the latter remains in communication with 

 the centrosphere. In the base of the beak the nuclear network is 

 loose and more open, while in the slender part it is drawn out into a 

 single and twisted thread. 



As soon as the beak has reached its definitive length the kinoplasmic 

 radiations undergo a remarkable change. The radiations which have 

 a direction similar to that of the beak begin now to bend or grow 

 backward, with the centrosome as a center, toward the nucleus, so that 



