7 74 Colchicine 



sets the meiosis so that abnormal metaphase I and irregularities occur 

 in subsequent stages. 



If prophases have proceeded normally, pairing is regular, but 

 colchicine introduced at the metaphase stage reduces spindle fibers. 

 Under these conditions, the bivalents remain scattered in the cyto- 

 plasm, and the separation of two homologous chromosomes proceeds 



TABLE 4.2 

 Relation Between Time of Treatment and Results 

 (After Dermen) 



Days After Treatment Results 



4 meiotic chromosomes in short 



broken chains; reduction of 

 chromosomes not noticed 



5 or 6 diploid and tetraploid pollen 



mother cells 



8 tetraploid and octoploid pollen 



mother cells 



11 polyploid microspores 



12 failure at me'.osis I and 11; hap- 



loid, diploid, tetraploid micro- 

 spores 



where each pair happens to lie. Since each homologous chromosome 

 of the pair is cleft and clearly separated, except at the region of the 

 centromere, a colchicine-anaphase I is characterized by two cruciform 

 "c-pairs" lying close to each other. The straight, cruciform anaphase 

 1 chromosomes are a contrast to normal ones at this stage. 



As the first telophase begins, chromosomes lose their staining 

 capacity, the chromatids remain connected at the centromere, and 

 the usual transformation to interphase between the meiosis I and II 

 takes place.ii^ The outlines of chromosomes are difficult to trace at 

 this stage and can be overlooked, making it appear that division II 

 begins without an intervening interphase, a prophase II, or a meta- 

 phase II. 



When the second c-meiotic division begins, chromosomes con- 

 dense and assume a prophase appearance. The contraction of the 

 chromatid proceeds in a prophase II. During this time the relic spiral 

 disappears and a chromosome of c-metaphase II comes into the pic- 

 ture. These chromosomes are held together at the centromere up to 

 late prophase; then they are straightened, and as fairly long chromo- 

 somes they separate from each other completely. The second c-meta- 



