CELL-DIVISION. 



35 



Fig. 13, I, J, shows several stages of the process just described in 

 two asci of Lachnea scutellata. 



While this is taking place the nuclear beak becomes smaller and 

 smaller until it is finally reduced to a mere thread in which chromatin 

 and membrane are no longer recognizable. The centrosome remains 

 for a short time as a deeply staining and sharply defined disk adhering 

 to the plasma membrane. Very soon it becomes free from the mem- 

 brane and is drawn back to the somewhat pointed nucleus, where it 

 appears as a saddle-like thickening upon the point of the nucleus, or 



FIG. 13. Free cell-formation in the ascus. 

 G, H, Erysiphe corn-munis. I, J, Lachnea scutellata. 

 G, the plasma membrane is complete ; nuclear beak withdrawn and centrosome saddle-shaped, and 



closely applied to the nuclear membrane. 



H, a mature spore with cell-wall ; centrosome closely applied to nuclear membrane at upper side. 

 I, J, portions of two asci showing several steps in process of free cell-formation in situ. (After Harper.) 



as a simple disk (Fig. 13, G, H). The nucleus now gradually assumes 

 its original spherical form, the chromatin passing into the structure of 

 the resting stage, while the centrosome remains closely adhering to 

 the nuclear membrane. 



It will be observed that in the specific case of cell-formation described 

 the plasma membrane is completed before the nucleus has reached the 

 resting stage, but in Lachnea (Harper, 1900) the daughter nuclei of 

 the eight-nucleated stage are completely reconstructed before the beaks 

 are formed. This may be, of course, a case of individual variation 

 and of only secondary importance. 



