Nuc/eus and Chromosomes 31 



the (hromosomal iuiiuIki in the restitution nucleus will be twice that 

 ol the nucleus betore a c-mitosis began. One important consequence 

 ol the c-niitosis in contrast to the normal nuclear mitosis is the in- 

 duction of polyploidy.^'-''*' But not all restitution nuclei become 

 polvj)loid. since the changes-- may start from a jiiophase or meta- 

 phase.^' In fact, many animal cells treated with colchicine are 

 arrested at metaphase. 1 he transformation from this stage docs not 

 lead to a restitutional polyploid nucleus, for in these instances other 

 changes occur. -■'• '^^ 



Finally, the most significant biological feature basic to all these 

 changes is reversibility.''^' After the colchicine in concentrations creat- 

 ing arrest becomes dissipated, the cell may recover; that is, a bipolar 

 nuclear mitosis again proceeds in the same manner as before an arrest 

 was induced. Such recovered cells will continue to divide thus as 

 long as the cell lineage retains that power. No permanent damage, 

 with few exceptions,'" to sjiindle mechanisms or chromosomes is ac- 

 quired from the arrested metaphase. Of course, the arrest may have 

 been so severe that changes in metabolism cause the cell to degenerate 

 and ultimately die, but our concepts of reversibility now refer to 

 those cases where there is complete recovery, a reversibility to the 

 bipolar mitosis. These can take place among i)lant and animal cells. 

 The recovery pattern like the whole c-mitotic sequence is unique and 

 notably imiform for many subjects. 



Since there is the reversibility potential, a restitution nucleus with 

 twice the number of chromosomes may regenerate its new spindle 

 mechanism. From a genetic view this is a most significant aspect of 

 reversibility, since the restitution nucleus with twice the number of 

 chromosomes gives rise thereafter to daughter cells, each with a poly- 

 ploid condition. 



By this jjrocedure of metaphasic arrest — c-anaphase, restitutional 

 polyploid nucleus, and recovery — the induced polyploidy is trans- 

 mitted to succeeding generations. This discovery has had inqjortant 

 ramifications in agricidttnal research. Whereas control over cell di- 

 vision woidd appear to be desirable for treating certain diseases, this 

 same control over cell division has entirely different, broad applica- 

 tions in agricidtiue. That is why a basic discovery in science can be 

 so widely used in other fields. 



2.3: Prophase 



First reports said that (olchicine had no iniluence upon pro- 

 phase.'''' -" Later by cinematographic record, no modification at pro- 

 phase was noticed.'"' A general belief developed that this jK)rtion of 

 niulear mitosis was not changed by the drug, for data obtained by 

 new methods from fixed and stained cells apj^eared the same for 

 treated and imtreated cases. 



