Nucleus and Chromosomes 35 



to move into the arrested metaphase. This would seem to be an 

 inhibition at prophase. Under optimum conditions for dose-time 

 relations, the maxinuun mctaphasic arrest is obtained in uianinials 

 at 8 to 10 hours following the injection of colchicine.''^ 



Amoeba sphaeronucleus may grow in colchicine without notice- 

 able changes. When colchicine is injected into the cytoplasm by 

 micropipette, action upon mitosis occurs. Amounts injected when 

 the nucleus is in prophase cause return to interphase. Continuous 

 photographic records verified this process. About l^per cent strengths 

 are needed to induce such chromosomal changes.-^ 



Different cells in Allium root tips show variation in degree of 

 polyploidy. Pericycle cells may contain several hundred chromosomes, 

 vet the cells at the tip, a meristematic area, will have the diploid num- 

 ber. Seventy-two hours of treatment with adequate concentrations do 

 not induce polyploidy among restricted groups of cells.*^'^- '-' This has 

 been called a prophase "resistance," characteristic of younger cells.s« 

 Practical significance becomes attached to this feature if polyploids 

 are to be induced without any diploid cells accompanying the new 

 tissues. Prophase stages are more involved than was formerly ac- 

 cepted. 



Two terms might be usefid in discussing prophase influences by 

 colchicine and other chemicals: (1) the pre-prophase poison which 

 prevents resting cells from entering the prophase, and (2) the pro- 

 phase poison, as described above, that inhibits the normal prophase 

 develoi:)ment and in exceptional cases causes a change to interphase. 

 Plants and animals differ with respect to the relative toxic action of 

 colchicine and these make a great difference in the inhibitions not 

 only of metaphase but of prophase as well. 



Prophasic arrangements that are held over from the previous telo- 

 phase are not disturbed in plants by concentrations that induce c- 

 mitosis, e.g., Dipcadifi'^ Yet this arrangement is upset in neuroblast 

 cells with concentrations that give typical arrested mitosis, ='" while in 

 mammals, prophase appears to be the most resistant period. i-^- ~^- ^i- ^^ 



Earlier opinion regarding prophase as always normal in the pres- 

 ence of colchicine must be modified. More information is needed at 

 this critical and difficult stage. Depending upon concentration and 

 the particular material treated, prophase stages are influenced by 

 colchicine. 



2.4: Colchicine Metaphase 



Again and again, after experiments w'ith animals and with plant 

 cells, the same conclusions were reached: colchicine changed the 

 nuclear processes at metaphase. With few exceptions, agreement is 

 unanimous, and the o])inions are usually formed around the lollow- 



