Colchicine 



475 



at right angles to one another to produce X-shaped figures. If 

 the treatment continues for a sufficiently long time the two chro- 

 matids separate at the centromere, and each lies in the cell as a 

 single chromosome. Thus the number of chromosomes is in- 

 creased from the diploid to the tetraploid. In some chromosomes 

 a distinctly double appearance is 

 noticed soon after the two chroma- 

 tids have completely separated. It 

 is the result of a ^'split" in anticipa- 

 tion of the division to follow the one 

 in which they are, and has probably 

 occurred just before the separation 

 of the chromatids into individual 

 chromosomes. This separation of 

 chromatids creates a cell with the 

 tetraploid number of chromosomes. 



From this colchicine-metaphase 

 the chromosomes may then go ap- 

 parently directly into a resting stage 

 or may go through the same ab- 

 normal performance one or more 

 times to form octoploid cells or cells 

 with even higher multiples of chro- 

 mosomes. Levan, in fact, has even 

 reported finding onion root-tip cells 

 with 500 to 1000 chromosomes as 

 the result of treatment with colchi- 

 cine. It might be added here that 

 it has become conventional to refer 

 to a metaphase resulting from col- 

 chicine treatment as a c-metaphase and to use such terms as 

 c-mitoses and c-treatment wherein the "c" obviously stands 

 for "colchicine." 



Various methods of applying the drug have been used. The 

 treated parts are usually seeds or growing buds, and the colchi- 

 cine is often applied in solutions varying from 0.1 to 0.8 per cent. 

 Treatment may be by soaking seeds, immersing a twig (Fig. 138) , 

 applying one or more drops to a bud, spraying with an atomizer, 

 and wrapping a bud in a string, one end of which is in the solu- 

 tion. Sometimes the colchicine has been applied in an emulsion 



Fig. 138. One of the meth- 

 ods used to apply colchicine 

 to a plant. The colchicine 

 solution is placed in a beaker 

 and the seedling is inverted 

 over it so that all the grow- 

 ing points are in the solution. 

 (From Nebel and Ruttle in 

 New York State Agricultural 

 Experiment Station Circular 

 183.) 



