Nucleus and Chromosomes 33 



mitosis, jxirticularly at prophase. Like the Tradescantia staminal hair 

 cell method, the drug can be administered when mitosis reaches a 

 certain stage; thus a new approach is made with animal cells. Time, 

 gross changes, and unusual developmental sequences can be charted. 



B\ this critical method the action of colchicine tipon jjrojjhase 

 was manifested in three distinct ways.'^^ First, strong concentrations 

 (50 and 25 X lO'^ M col.), applied at late and very late prophase, 

 caused the chromosomes already partially formed to revert to an 

 earlier dispersed phase. Second, lowering the concentration (2.5 X 

 10 •' M) induced precocious reduction in the relational coiling and 

 an unusual contraction of the chromosomes before the nuclear mem- 

 brane disappeared. At this concentration, prophase chromosomes, 

 normally fixed with centromeres at the polar side of the nucleus, were 

 disoiiented. By microdissection methods, the polar fixation at pro- 

 jjhase was tested."'' Colchicine, in proper concentration, destroys some 

 factor associated with this fixed position. Third, additional decrease 

 in concentration (1.9 X 1^^'' ^i) applied at prophase disposes the 

 chromosomes into the "star" formation as soon as the nuclear mem- 

 brane disappears. These stages may develop into a multij)le-star 

 phase, and from this formation chromosomes settle out to the bottom 

 of the cell. These three conditions show that colchicine induces 

 changes at prophase when certain concentrations are used. These 

 changes are revealed when continuous records can be made.-'-' 



Thus colchicine may act upon chromosomes at prophase, causing 

 interphase loss in relational coiling, contraction, destruction of 

 intranuclear orientation, and predisposing the chromosomes to a star 

 formation. These comparisons required a special technique able to 

 focus attention ujK)n specific stages, using a wide range of concentra- 

 tions, and then following the successive development from one stage 

 to the next. •''' 



Pollen grains planted in colchicine sucrose-agar^^- ^" provide a 

 special method for observing the effects of strong concentrations (1 

 per cent) upon prophasic stages. Each grain at the time a cidture 

 starts, begins with a nucleus in prophase. Pollen tubes grow and the 

 cell lives for a time, but the jjrophase goes into interphase and 

 does not move into an arrested metaphase. These unpublished data 

 were collected from treated and untreated cells fixed and stained at 

 given intervals. 



Analyzing percentages of prophases, trcatetl and untreated, there 

 is noted a proportional decrease in the relative percentage of pro- 

 phase as the experiments continue."-^ Inhibition of prophase is indi- 

 cated with concentrations that cause arrest at metajihase (0.01 per 

 cent). This decrease for AUiutii begins after twenty-four hours"" 

 (Table 2.1). At this period the c-metaphases have reached a peak.''" 



