﻿1903] BEHAVIOR OF THE CHROMOSOMES 261 



I 



Other hand, should the spirem segment in some places at the 

 points corresponding to the angles of the V's, and at others which 

 represent the points of contact of the free ends of the V-shaped 

 chromosome, then some of the chromosomes of the second 

 division would be composed of sister segments while others 

 would not. If either of the last named possibilities be true, it 

 might very easily happen that sister segments would ^o to the 

 same granddaughter nucleus, a condition that might furnish a 

 probable basis for a greater variation. Even though the latter 

 supposition be true — that some or all of the chromosomes are 

 not sister segments — it is possible that the results would be the 

 same, for the spindle, or whatever part of the cell that has to do 

 with the distribution of the chromosomes, may be able to prevent 

 any such mixing by distributing to the granddaughter nuclei 

 those chromatin elements which would unavoidably go to each 

 if every chromosome were identical with the pairs of sister seg- 

 ments of the preceding division. 



But since the chromosomes lose their identity in the daug^hter 

 nucleus, neither of the foregoing suppositions can be objectively 

 demonstrated. This is not possible, as yet, even m those cases 

 m which the spirem is very regular or in plants with fewer chro- 

 mosomes, and the possibility is still farther removed in those 

 cases of more frequent occurrence in which the spirem is very 

 irregular. 



In the foregoing statements the writer does not intend to con- 

 vey the idea that he rejects the older view, but the doctrine is 

 advanced largely as a probability which seems to have some 

 basis in fact. The older view, that the chromosomes of the 

 nuclear plate of the second mitosis are identical with the pairs 

 of granddaughter segments of the first division, is the simpler 

 hypothesis, involving fewer complications, and for that reason it 

 «iay be more readily accepted. Its truth, however, can be no 

 more definitely demonstrated than that which I have suggested 

 as a possibility, for there is no known angiosperm. so far as the 

 writer is aware, in which the chromosomes of the first division 

 do not lose their identity in the daughter nucleus, and we do not 

 know with absolute certainty whether the daughter spirem seg- 



