2l6 J. MCA. KATER. 



manner described above and there remains in the place of the old 

 nucleus a mass of chromosomes with one end of each still im- 

 bedded in the apparently homogeneous nucleolus and the other 

 end projecting freely (Fig. 18). In order to return to the point 

 at which this description started the chromosomes have only to 

 separate. This is a gradual process. Cases may be observed 

 in which only one or two chromosomes have become entirely 

 separated from the rest of the mass (Fig. 19). From this condi- 

 tion we go, chromosome by chromosome, to the point where all 

 or nearly all of them are separate (Fig. 20). 



The chromosomes of Phaseolus are too small to be favorable 

 for a study of the process of splitting and since that is not the 

 subject of this work no careful attempt has been made to follow 

 that phenomenon. 



HISTORICAL AND DISCUSSION. 



Reconstruction of Daughter Nuclei. Phaseolus has been used 

 by several investigators in studies of mitosis and nuclear struc- 

 ture. Wager (1904) has given a very excellent account of mitosis 

 in this plant and, in view of the fact that he did not properly 

 interpret his observations, the accuracy with which he figured 

 them is remarkable. Although he did not follow the nuclear 

 changes in the telophase closely enough to show conclusively 

 that the linin strands, which apparently connect the nucleolus 

 with the nuclear membrane in the resting stage, are the linin 

 sheaths of chromosomes and that the chromosomes retain their 

 individuality through the resting period, he, nevertheless, gives 

 several very suggestive figures. Figs. 29 and 30 in his account 

 are practically the same as Figs. 4 and 6 in the present work. 

 The principal object of his study was to discover the origin of 

 the nucleolus and his conclusion that it arises by the joining of 

 non-vacuolated ends of chromosomes has been clearly verified 

 by the present observations. 



Wager observed and figured telophase conditions which, if they 

 had been carried a little further, would have shown conclusively 

 that the chromosomes of this plant are continuous from one 

 mitosis to the next. He merits credit for being the first to make 

 such clear observations of this phenomenon even though his 



