94 Colchicine 



strikin^• and significant biological characteristics demonstrated when 

 dividing cells of animals and plants come in contact with optimal 

 doses of colchicine. 



^.8—i: Recovery in j)Iants. Allium root tips transferred to pure 

 water after specific exposures to colchicine are excellent materials for 

 tracing recovery of the spindle mechanism. Very slight toxicity, if 

 any, results from an exjjosure sufficient to inactivate the spindle com- 

 pletely. Usually 12 to 24 hours in \\ater gi\e adequate time for first 

 recovery stages. '^^^ "•''• ^^- ''i- ""•■ -i- -^ 



The regeneration of spindle runs a characteristic course, proba- 

 bly representative of many plant cells. But most work has been 

 done with Allium cepa L. specifically, and with root tips rather than 

 stem tips, generally. By a characteristic course is meant the sequence 

 of chromosomal groups from full c-mitosis to partial c-mitosis, then to 

 bipolar spindles. During this course the obvious abnormalities appear 

 in terms of normal mitosis.-^-^- -^f'- '"■'■ -'■ '■'■ •^■''' "!• ^"'' '• -!• -'^ First, the chro- 

 mosomes group into what may be called midtijilc star formations 

 (Figs. 3.6 and 3.8) . There is no connection between the various stars 

 of a single cell. The chromosomes may be somewhat clumped together. 

 Shortly thereafter, asynnnetrical and loose spindles appear. 



Cells with unusually high numbers are followed in the transition 

 to normal mitosis. Extremely large cells with high numbers appeared 

 in tissue cultures of plan.t cells.*'- The first hint that a cell is on the 

 road to recovery shows in the telophasic stage. Chromosomes are not 

 condensed into one nucleus when first observed. Later each nucleus 

 becomes perforated and filled with canals. Next the grouping of 

 nuclei of a large cell is like a multiple cell.'^i containing as many as 

 twenty stars. ^^ Perhaps each star represents a regenerating spindle 

 area. When telophase sets in, fibers running between each grouj) lead 

 to cell wall formation (Fig. 3.9) . I'hus, the large restitution nucleus 

 containing many chromosomes, becomes divided into as many as 20 

 small cells. ''!• ''- 



The ob\ ious reduction to many small units means reduced dnomo- 

 somal numbers. While this is "somatic reducticjn," it does not corre- 

 sjjond to reduction through meiosis, except in the numerical changes. 

 Certainly no qualitative genetic reduction takes place such as occurs 

 in meiotic j^rocesses.-^*' 



After 3(i hours most cells have run their normal course. A dia- 

 gram correlating length of exposure to time for regeneration and com- 

 pleted reccjvery, has been constructed.^'' Fhe exposures, covering 7 to 

 30 minutes, rec[uire between 12 to 24 hours for the first spindle regen- 

 eration, and 36 hoius for regular sj^indle. An increasing exposine, 2 

 to 72 hoins, retards sjjindle regeneration to 24 hours, and delays com- 

 plete recovery to 36 and 48 hours. This means that the longer the 

 exposure, the longer the time for recovery. 



