92 KANSAS UNIVERSITY SCIENCE BULLETIN. 



While the reconstruction of the nuclei has been in progress, 

 several changes have occurred in the spindle and the cytoplasm. 

 As soon as the concentration of the cytoplasm is complete the 

 spindle broadens out somewhat. Figure 23 shows a maximum 

 bulging, while figure 22 is perhaps a minimum. Figure 22 

 shows an unusual phenomenon in the process; the majority of 

 the central spindle fibers (only the central fibers now remain) 

 seem to have become free at their polar ends and to have short- 

 ened towards the center, staining very darkly in this region. 

 The threads disappear as soon as the cell walls are formed. It 

 is difficult to determine what the bulging out of the spindle and 

 the concentration of the threads and cytoplasm signify, but it 

 seems probable that the threads contain some substance useful 

 in the construction of the new cell wall. This suggestion is in 

 line with the work of Strasburger (4) and Haberlandt (5), 

 who have discussed this phenomenon of the spindle in detail. 

 The rate at which these processes occur varies. One may 

 find a nuclear membrane before the cell plate has started (fig. 

 20), or he may find the cell plate well started while the chro- 

 matin is still in the loose daughter "skein" (fig. 19). 



GENERAL CONSIDERATIONS. 



Ach7'omatin and Archoplasm. — In regard to the origin of 

 the spindle Schaff'ner concludes that, in root-tips of the onion 

 and of Sagittaria, at least, the multipolar spindle is due 

 either to pathological causes or to ''improper manipulation 

 in preparing the sections," and that a bipolar spindle is formed 

 not by the transformation of a multipolar stage but under the 

 influence of a centrosome and centrosphere as commonly de- 

 scribed for animals. As previously stated, I find no evidence 

 whatever for concluding that such archoplasmic structures are 

 present. 



Although no traces of a multipolar spindle have been seen 

 here, it is not necessary to assume that a centrosome is present 

 to guide the formation of the bipolar spindle, as the fibers them- 

 selves may possess sufficient directive energy to bring about 

 the bipolar form. 



Individuality. — A single bit of evidence was found in support 

 of the theory of individuality of the chromosomes in vegetative 

 cells. In several of the cells there is an unusually long chromo- 

 some, m, in general dividing before the others in the cell. Al- 

 though this meager bit of evidence is by no means conclusive. 



