INDUCED POLYPLOIDY I 55 



by experts are in many cases tetraploids. If we limited competition among 

 Iris to diploids, we would at once eliminate many of the most prized varieties. 

 Among many horticultural varieties, the triploids and tetraploids are well 

 known for their valuable contributions in one or several ways. 



A NEW ERA. The rediscovery of colchicine. Realizing, then, both theoretical 

 and practical implications of mitotic arrest and polyploidy, it is not surprising 

 to learn that the development of good methods for inducing polyploids con- 

 veniently and efficiently should attract so much attention (Dustin, 1934; 

 Ludford, 1936; Gavaudan et al., 1937; Blakeslee and Avery, 1937; Nebel 

 and Ruttle, 1938; Eigsti, 1938; Levan, 1938; Havas, 1940; Eigsti and Dustin, 

 1955). Some speculations were made beyond the factual limitations. Such 

 was the unusual interest created when colchicine became known as an agent 

 for doubling the number of chromosomes. 



This chemical, colchicine, was demonstrated by Levan (1938) to be specific 

 and efficient in creating polyploid restitution nuclei, opening a new era for 

 induction of polyploidy (Eigsti and Dustin, 1955). The action on dividing 

 cells of roots, stems, pollen, and other embryonic tissues led to a new and 

 important tool for plant scientists. 



Colchicine was not a new idea for arresting mitosis. A heat treatment was 

 suggested by Belling in 1925 and was successfully applied with maize (Ran- 

 dolph, 1941). Also, cold-heat shock methods were useful in studying poly- 

 ploidy at the chromosome laboratory at Svalof, Sweden. Levan reported that 

 this elaborate machinery for producing polyploidy by heat and refrigeration 

 became museum pieces overnight after colchicine methods had been developed. 

 This rediscovered chemical, first observed by Pernice in 1889, was so superior, 

 so effective, and so readily applied that its use with many kinds of plants was 

 assured. Laboratories already investigating polyploidy switched to the new 

 procedure, while in other places new programs were started that had not been 

 previously conceived along the lines of polyploidy breeding. It was hoped that 

 new varieties would be developed quickly. The acceptance of this method of 

 plant improvement was widespread, and numerous papers were published 

 beginning in 1938. Something new in research had arrived according to 

 Wellensiek (1938), who reported a "colchicine fad." 



Colchicine freed of its impurities is a white powder obtained from any one 

 of a number of species of plants, but notably from the genus Colchicum 

 (Cook and Loudon, 1951). Pharmacists recognize only C. autumnale L. as 

 the official drug plant, although C. luteum Baker is admitted in India, where 

 this spring-flowering species is abundant and is also an excellent source for 

 the drug (Eigsti and Dustin, 1955). 



The pure substance is in the form of needles and has a melting point of 

 155°C. It is colorless, readily soluble in water, chloroform, or alcohol. While 

 colchicine is often classified as an alkaloid, such classification is open to ques- 

 tion on the basis of additional chemical study of the past two decades as re- 



