282 Colchicine 



characteristics that place the tyjie closer or farther from one of the 

 two classes. Table 12 of their work is worth considerable attention 

 for those interested in the classification of polyploids. As would be 

 expected, the known polyploids form an intergrading series from the 

 extreme autoploid to the amphiploid, which is a completely diploid- 

 ized type. Colchicinc-induced polyploids cause increasing inter- 

 gradation as more and more examples appear. 



For purposes of reviewing the colchicine-induced polyploids, re- 

 sorting to taxonomic authority has served a very useful purpose. If 

 the polyploid has been a product of doubling a species hybrid in- 

 volving accepted species, then the type is considered amphiploid, 

 while the diploids made tetraploid are autoploid. Admittedly the 

 system is artificial and does not delve into the real problem that 

 makes a polyploid what it is. However, with the view of handling 

 large amounts of data and many polyploids, this method of classifica- 

 tion is simpler. At no time has the basic feature of the segmental 

 allopolyploid or its significance been overlooked. Those character- 

 istics that are peculiar to the segmental allopolyploid are important 

 practically and in certain evolutionary aspects. 



11,5: Principles of Polyploid Breeding 



Within five years, from 1938 to 1942, examples of all the major 

 agriculture species of Sweden were converted into polyploids.^fi. «9. i 

 In other places throughout the world vast numbers of polyploids 

 were created at about this same time. Colchicine accounted for many 

 of the new polyploids, but few of these could be used in agriculture. 



7.3, 65, 49, .54, 56, 57, 63, 35, 62, 44, 19, 21, 22. 30, 32, 3, 5, 8,9.15, 16 Xllis may COmC aS 



a shock to i)ractical agronomists. A re-examination of the principles 

 basic to polyploid breeding was needed. Since so much material was 

 at hand, polyploids were used to test a number of points about chro- 

 mosome doubling as a method of plant breeding. The principles enu- 

 merated below have been stated directly as such or indirectly through 

 the work of a number of investigators. 



The application of colchicine permitted the production of large 

 numbers of polyploids from diploids. One would expect these new 

 polyploids to replace the standard diploid varieties.''^ However, 

 artificially induced polyploids are, at the beginning, "raw" polyploids 

 without exccption.^*^ Such types are generally unselected, so the task 

 of jjlant breeding has only begun after the polyploid has been made.'**' 

 Too many investigations disregarded the principle of raw polyploids 

 and tested the tetraploids against the selected diploids. Naturally, 

 the tetraploids failed to measure up to diploids in all-around per- 

 formance. What is even more surprising is the condemnation of 

 colchicine when tetraploids, apparently as raw polyploids, failed to 



