﻿1903] BEHAVIOR OF THE CHROMOSOMES 267 



spirem formed at once from the segments of the daughter chro- 

 mosomes. The reticulation continues, at least in many cases 

 observed, until a structure is reached that is certainly very near 

 that of a resting nucleus. Fig, jy represents a nucleus seen 

 from the pole. If the same nucleus were observed from the 

 side, at this or even a little earlier stage, its chromatin would 

 present the appearance of a rather thick and irregular spirem. 

 There are phenomena in Tradescantia which would suggest 



, that the daughter spirem or parts of it are formed double, but 

 all the evidence taken together seems to indicate that only a 

 single spirem is the result. Daughter nuclei were observed in 

 which certain parts of the spirem, or chromatin thread, seemed 

 to be double, while other parts showed nothing of a double 

 character. The chromatin of the daughter nucleus does not 

 form the regular and uniform spirem to be observed in other 

 monocotyledon ous species and in Podophyllum, and for this 

 reason the differentiation of the chromosomes is followed with 

 greater uncertainty. With the approach of the second mitosis, 

 the chromosomes are differentiated and lie distributed in the 

 nuclear cavity before the disappearance of the nuclear membrane. 

 They are often very irregular in shape and connected by deli- 



. cate linin threads. Even when arranged in the nuclear plate, 

 they present an irregular, lumpy, and twisted form. In those 

 cases in which the chromosomes are most regular, each is seen to 

 consist of a pair of rod-shaped segments which are either straight 

 with only a slight bend at one end, or more or less undulating 

 and twisted [fig. jg). As in Lilium, some of the chromo- 

 somes are oriented radiall)^ and some tangentially upon the 

 spindle. 



It may be that the two segments composing each chromosome 

 are sisters, and that the chromosomes are identical with the pairs 

 of granddaughter segments of the first division, but the possi- 

 biUty of an objective demonstration of this supposition seems 

 out of the question. 



The process of the second karyokinesis in the pollen mother- 

 cells of other plants seems to suggest strongly that the division 

 c>f the daughter nuclei has some other purpose than merely the 



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