cytokinesis, to cells with less than the diploid number of chromosomes. 

 Later, Wilson. Hawthorne, and Tsou (1952) noted similar "reduction" 

 figures in untreated onion roots (Figure 5-9). They referred to these as 

 "split figures" and, in some cases found the metaphase spindle to be 

 double. Usually, since the double spindles were close together and in the 

 same plane, anaphase separation and telophase transformation led to 

 the usual binucleate condition. Occasionally, however, the two spindles 



Figure 5-8. Photomicrograph of Polytene Metaphase in Meristematic 

 Cell of Pea Root. (Courtesy of Dr. Jack Van't Hof, Michigan State Uni- 

 versity.) 



were tipped relative to each other, which resulted in tri- or tetra-nucle- 

 ated cells. Only in rare cases, however, were viable cells with subdiploid 

 numbers found. Whether or not such "split figures" tend to separate 

 homologues is not clear. Wilson and Cheng (1949) did find more cases 

 of homologous separation in Trillium than expected on a random basis. 

 Whether such "split figures" result from multiplication of spindle foci 

 or chance alignment of spindle fibers is not known, but the fact that such 

 separations are found before spindle organization suggests the latter. 



Deviations from "normal" mitosis appear to be characteristic in some 

 tissues. For example, all of the departures from norm which have been 



132 / CHAPTER 5 



