84 Colchicine 



exploded mctaphase and ihat complete spindle inacti\ation is funda- 

 mental to the unoriented type or lull c-mitosis. 



Presence of the pseudospindle"^ or the achromatic sphere'^S' ' (Fig. 

 3.9) has helped to explain the scattered arrangement in some cases, 

 notably in Allium root tips (Fig. 3.7). C-pairs are closely appressed 

 around an achromatic sphere. But comparable cells in regenerating 

 liver exhibit excellent exploded metaphases without a stainable 

 sphere. Other scattered types are not comparable to the special case 

 of All i inn. 



The assumption- that a single centrosomic spindle operates in 

 pushing the chromosomes to the periphery of the cell is hardly ten- 

 able, for staining has not proved the case, nor have the other tech- 

 niques subtantiated such mechanisms. It would hardly be consistent to 

 classify as an unoriented type, one that had such a mechanism as a 

 central spindle pushing the chromosomes to the edge. 



Whatever the final answer will be as to their disposition, they 

 seem profusely scattered, and seem to lie in the cytoplasm as if each 

 repulsed the other. 



The exploded metaphases are a striking type.^^' ^''> They would 

 seem to result from the total inactivation of both the continuous and 

 the chromosomal fibers. 



The ball metaphase is more common than the exploded mcta- 

 phase; it increases in frequency as the concentration increases. A 

 toxic or poisoning action is logically the basis of a ball metaphase. 

 The chromosomes are defmitely unoriented and are often massed in 

 a clump. For that reason the c-mitosis has been called ( linnpcd, a t\pe 

 related to the loall metaphase.^"' '^~ 



Prophase-metaphase formations (Fig. 3.2) are more nearly de- 

 scribed by the term arrested prophase (cf. Chapter 2) , for they re|)resent 

 leftOAcr prophasic arrangements. AVith no spindle action, chromo- 

 somes remain stranded in a pre-prophasic arrangement.^^'* In fact there 

 is complete inactivation. Prophase orientations are not necessarily 

 disturbed by colchicine, as noted for Dipcadi.''-' Here the chromosomes 

 are disposed in a pattern determined by the previous telophase. If 

 the concentration is partially inactivating, a star metaphase results; 

 total inactivation leads to the prophase-metaphase type.-^- '» The pro- 

 phase-metajjliase merges into the ball metaphase and clumped meta- 

 phase depending on the concentration. There may be return by re- 

 covery to a multinucleate cell. The prophase-metaphase and clumped 

 c-mitosis seem to be more characteristic of meristematic cells of stems 

 than of roots. ''^ 



Distributed c-mitoses have attracted nuich attention because they 

 were described as a "somatic meiosis" (cf. Chajiter 2) . These are a 

 subtype of the exploded metaphase. The main diiference between 

 exploded and distributed metaphase is seen in the disposition of the 



