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INTRODUCTION TO CYTOLOGY 



the positions in which the remaining portions happened to He during the 

 metaphase. Long chromosomes, because of their trailing ends, may thus 

 present a rather confused picture during these phases (Fig. 56). The 

 attachment regions reach the poles in advance of the other portions, often 

 before the trailing ends have separated at the equatorial plane in the 

 case of very long chromosomes; such chromosomes may shorten consider- 

 ably after their ends draw away from the equator. Eventually all the 

 chromosomes lie more or less parallel in two fairly compact groups 

 between which the spindle substance may be seen. In certain cases 

 persistent nucleoli have been observed to pass poleward. 



In the telophase each group of chromosomes reorganizes as a metabolic 

 nucleus. This involves a series of changes which in many respects are 

 the reverse of those seen in the prophase. During the anaphase the 



12 3 4 



FiQ. 55. — Development of metaphasic arrangement of chromosomes. Spindle-attachment 

 regions indicated by dots. P, "pole field." {.After Belaf, 19296.) 



chromosome matrix is highly chromatic, but as the telophase begins this 

 chromaticity decreases, so that the chromonemata again become evident. 

 Furthermore, these chromonemata may be double as the result of a 

 splitting which has been shown in some cases to have taken place shortly 

 before the metaphase. Meanwhile the nuclear membrane, karyolymph, 

 and nucleoli appear. As the two nuclei grow, the chromonemata tend to 

 become less basichromatic and join to form the more or less continuous 

 and uniform reticulum characterizing the metabolic stage. 



In rapidly growing tissue with the mitoses occurring in quick succes- 

 sion, as in the meristem of the root tip, the telophasic changes often are 

 not carried far enough to obscure the limits of the chromosomes in the 

 reticulum before the changes of the ensuing prophase begin. In such 

 nuclei it can often be seen that many or all of the attachment regions 

 occupy a rather restricted area ("pole field") at the side away from 

 the equator (Fig. 55), and that the parallel arrangement of the chromo- 

 somes assumed in the anaphase persists until the next prophase. The 



