280 Colchicine 



When colchicine was discovered as a tool for doubling the chromo- 

 somes, it was believed by many that evolution was about to be 

 speeded up out of proportion to anything known. The tool, col- 

 chicine, did in fact remove a serious bottleneck^'? in permitting a 

 doubling of the species hybrid by a new and more efficient method 

 than ever before available. Many newcomers to the ranks of new 

 species have been produced; this is evident if we compare our list 

 of amphiploids produced since 1937 with the list made before that 

 date. There is no doubt of a speeded-up tempo, but unless one 

 possesses a broad and deep knowledge of cytogenetics, he will fail to 

 see that the expected "miracles" have been forthcoming. The intro- 

 duction of a new variety of wheat by ordinary standards requires 

 about 15 years.«« To produce a new polyploid variety is as difficult, 

 if not more so. 



11.4: Classification of Polyploids 



The two principal classes of polyploids are (1) autoploids derived 

 from homozygous diploids, e.g., tetraploid maize,''o and (2) amphi- 

 ploids, like Raphanobrassica,-'^ resulting from hybridization. These 

 two types are not difficult to distinguish. They are extremes with the 

 autoploid carrying four sets of homologous chromosomes AAA A, and 

 the amphiploid. two diploid sets AA and BB. The difficulties in 

 classifying polyploids arises when dealing with examples between the 

 different types, that is, polyploids with both autoploid and amphi- 

 ploid characteristics.'''^ There are many cases - and more are being 

 made continuously — that are intcrgrading types and, as such, are not 

 easily classified into the autoploid or the amphiploid category. 



Problems of classification in polyploidy are similar to those in 

 other systematic studies. For example, everyone agrees on which 

 individuals of the species belong to the Mammalia and the Sperma- 

 tophyta; however, among the microorganisms a classification problem 

 has new difficulties. Since the bacteria are so widely studied in re- 

 lation to human disease, the medical bacteriologists find it illogical 

 to group them with the fission fungi, or Schizomycetes, of the plant 

 kingdom. As a matter of fact, some bacteria do have plant and animal 

 characteristics, and so present a distinct problem in classification. 

 Likewise in polyploidy, the borderline cases have characteristics that 

 are both autoploid and amphiijloid. As colchicine increases the 

 number of polyploids, the intergrading types are increasing at the same 



lime. 



The artificially induced hexaploid Phleurn nodosum, created by 

 colchicine,-^^ ^ad^y be used as an example of the disagreement on clas- 

 sification because the true nature of its autoploidy is in disinite. 

 When all the evidence is carefully reviewed in this case, the complex- 



