Amphidiploids 459 



though the exact species involved have not been proved con- 

 clusively, Clausen and his co-workers believe that the original 

 parents of Nicotiana tabacum were closely related to A^. syl- 

 vestris and N. tomentosijormis. Numerous other amphidiploids 

 among cultivated plants have been reported, and many of them 

 have been listed and discussed by Schiemann. 



Intergeneric amphidiploids have been produced between closely 

 related genera. Probably the best known is Raphanobrassica, 

 Karpechenko's synthesized hybrid between a radish (Raphanus) 

 and a cabbage (Brassica). Each of the parental species has 

 nine pairs of chromosomes and the amphidiploid had eighteen 

 pairs. The latter was perfectly fertile, as might be expected 

 from the nature of its meiotic behavior. All the gametes have 

 nine radish and nine cabbage chromosomes. 



A series of amphidiploid hybrids between wheat (Triticum) 

 and rye (Secale) has also been studied. These amphidiploids 

 constitute a new genus, Triticale. Miintzing examined six such 

 strains which differed in the particular wheat and rye biotypes 

 that formed the parents. In pollen fertility they varied from 

 61.8 to 92.5 per cent fertile, although they varied within the 

 strain from year to year. Two of the strains showed bivalenls 

 and univalents at the first meiotic division (Fig. 132), with the 

 frequency of univalents higher in one strain than in the other. 

 Higher configurations were extremely rare. The various strains 

 differ in height, in vigor, in winter hardiness, and in their qual- 

 ity in baking. Apparently the properties of a particular strain 

 of Triticale depend less upon their polyploid nature as such than 

 upon the particular biotypes of the wheat and rye plants that 

 were their parents. 



Other amphidiploids have been made among the Triticenae by 

 Sears. Eighteen amphidiploids from ten species in which the 

 haploid number of chromosomes was seven were synthesized, 

 and seven of them were from intergeneric crosses involving the 

 genera Triticum, Haynaldia, and Aegilops (Fig. 133). They 

 were generally intermediate between their parents in their mor- 

 phological characters and varied in fertility from very highly 

 sterile to very highly fertile. At meiosis most of the configura- 

 tions were bivalents. However, there were some univalents, tri- 

 valents, and quadrivalents in almost all, and a few of the amphi- 



