LIFE HISTORY OF PINUS 23 



for Symflo car-pus^ but they remain always irregular and jagged 

 in outline (figs. 8 and 9). Whether there is one continuous 

 thread or more than one could not be determined with certainty, 

 as the coil is at first very densely massed, and free ends might 

 be obscured. When the loose skein fills the nuclear cavity 

 more than one spireme can usually be detected, but the indica- 

 tions are that this effect has been produced by the microtome 

 knife. At certain places the coils of the spireme run together 

 and appear to be more or less anastomosed. Such a point of 

 contact alwa3's indicates the position of a nucleolus which has 

 become almost obscured by the massing of the thread about it, 

 figs. 9, 13 and 15. Not all the nucleoli are found thus associ- 

 ated with the skein, but in those cases in which they are free 

 from the coils of the nuclear thread their capacity for staining 

 has generally been greatly reduced (figs. 9, 11 and 15). 



As soon as the chromatin-band has become loosely wound 

 about the entire nuclear cavity, longitudinal splitting occurs, 

 and the segmentation of the spireme becomes apparent (fig. 10), 

 but transverse fission is not completed until the longitudinal 

 division has taken place (fig. 11). The segments are long, 

 coiled, and present various appearances. Whether they 

 correspond in number to the number of chromosomes eventu- 

 ally formed, I could not ascertain with any degree of certainty, 

 since they are so long and closely intermingled in the nucleus 

 (fig. 11). Most of those shown in figs. 12 and 12, «, were taken 

 from sections through the edge of nuclei, and, while they rep- 

 resent the looped and twisted condition of the chromatic seg- 

 ments at this time, they have in many instances been cut during 

 sectioning so that only a portion of most of the segments 

 appears. From a study of many nuclei containing chromatic 

 threads similar to these, it is evident that the looped figure has 

 not been formed by the bending on itself of one of the longi- 

 tudinal halves of a segment. There are no indications that the 

 sister-halves of any portion of the nuclear band ever become 

 entirely disassociated. They may separate widely at one or 

 both extremities, but at some point along the thread, an inti- 

 mate relation is permanently maintained. The loop arises, 

 therefore, by the complete fusion of the sister-threads at one of 



