48 Colchicine 



of chromosomes. Not only the comparative sizes of chromosomes 

 within a set can be jtidged (Fig. 2.4D) , but the relative differences be- 

 tween the two arms of a chromosome can be estimated.^^ For these 

 reasons the pretreatment of chromosomes by colchicine was sug- 

 gested'o and there followed an important advancement in cytological 

 technique which now makes it possible to study chromosomes, par- 

 ticularly among root tips, with much greater accuracy. i"- ''•"■*• *'» Scat- 

 tered chromosomes in the pollen tube led to the discovery of the 

 natural polyploid Polygonatum cominiitatum.^^ If the chromosome 

 pairs are studied, duplication of a haploid set is obvious (Fig. 2.4D) . 

 Since the generative nucleus is haploid, there should theoretically be 

 only one of each chromosomal type. But each type was repeated, typi- 

 cal of tetraploids (Fig. 2.4D) . Then any related diploid should have 

 only one of each type. This was found by extending the study to 

 other representatives of the genus. The colchicine technique was use- 

 ful for this cyto-taxonomic study.-^^. 



2../-5.- Duration of colchicine-initosis hi (niinidl cells. Degenera- 

 tive changes are frequent in arrested metaphases of animal cells, 

 especially in mammals.' Their mechanism, which may be of some im- 

 portance when colchicine is utilized in the treatment of abnormal 

 growth (cf. Chapter 10) is not clearly understood. As explained 

 in further chapters, colchicine has been extensively used as a tool for 

 the study of growth. It is impossible to reach precise conclusions if 

 the duration of a given c-mitosis is not known. Direct observations 

 can be made only in limited cases excluding all sectioning materials. 

 From the study of sections, it appeared from the early work that 

 within 24 hours or less, an arrested metaphase either recovered, or 

 underwent destruction.-'^- *^^ 



In cold-blooded animals, colchicine is probably metabolized much 

 more slowly (cf. Chapter 7) . In Siredon, after a single injection, a 

 great number of arrested mitoses could be seen in the spleen (Fig. 

 2.2) . This was apparent five days after the injection, and lasted for 

 about ten days.^-* In Triturus, seven days after colchicine had been 

 applied to the cornea, abnormal mitoses with scattered contracted and 

 unoriented chromosomes have been reported (Fig. 2.7) .'^ 



However, a precise study of the duration of colchicine-mitoses in 

 the larva of Xenojnis led to the conclusion that destruction took 

 place much sooner. This was calculated by an indirect method.^^ 

 From data of short treatments with colchicine and from direct ob- 

 servation, it was foimd that epidermal mitoses lasted about 100 

 minutes. It was further assumed that the normal prophase duration 

 of about 25 minutes was not modified by colchicine. In colchicinized 

 animals the relations between the numbers of prophases and colchi- 

 cine-metaphases and the average duration of each should be equal. 



