SPECIAL NUCLEAR PHENOMENA. 37 



The cytoplasm of the ascus is homogeneous and spongy, with no 

 large vacuoles or inclusions at this stage. The nuclei lie rather close 

 together, separated by a less distance than their own diameter through- 

 out the early development of the ascus (figs. 31, 32). They fuse at a 

 stage just before the penicillate cells begin to sprout out on the upper 

 surface of the perithecium. As they approach each other to fuse, the 

 central bodies may be very variously placed with reference to each othei 

 and to the plane of contact of the nuclei. I have been unable to find any 

 evidence that the position of the centers influences in any way the 

 approach of the nuclei or determines the point of their first contact. 

 The centers are frequently placed facing each other (fig. 31). In 

 other cases they are separated by 90 or more degrees on the surface of 

 the nuclei (fig. 33). Occasionally, just prior to fusion, one nucleus 

 may be pulled out into a pear-shaped body, with the center at its nar- 

 rowed end, and this narrowed end may be extended beside the second 

 nucleus. In this case, however, the centers may still be separated by 

 half a circumference from each other. 



The nuclear membrane disappears at the point of contact, and the 

 chromatin and nucleoles of the two nuclei thus come to lie in a common 

 cavity. In fig. 35 one chromatin system is drawn out into a long cone, 

 the central body apparently having pushed ahead into the second nucleus, 

 dragging the chromatin after it. The chromatin threads maintain for 

 some time their independent orientation about their separate central 

 bodies (figs. 35-37). The outline of the double nucleus may for a time 

 show a constriction in the plane of fusion ; later it may round out on one 

 side before it does on the other (fig. 38) . The centers are still variously 

 placed with reference to each other. In rare cases they may even be 

 for a time exactly opposite each other on the surface of the nucleus, 

 with their respective chromatic systems extending toward each other, 

 suggesting the formation of a spindle. Frequently, however, the fusion 

 occurs in such a way that the centers are brought close together at once. 



Wherever the centers may be, the masses of chromatin show no 

 tendency at this stage to combine; they may be in contact with each 

 other, but are simply crowded together and show no tendency to unite. 

 Later, in all cases the centers are found lying side by side in preparation 

 for fusing, but the chromatin-thread systems are still quite independent 

 (fig. 38) . At this stage, as at the stage just before fusion, it is possible 

 to count approximately the number of threads extending back from each 

 center. There are, as a rule, at least four or five threads lying in about 

 the same focal plane near the median optical section of the system. By 

 focusing up and down at least four more threads can be made out which 



