抄録
The species N. umbratica reported from Australia (Burbidge 1960) is unique in the genus Nicotiana having a chromosome number of 2n=46. Intersubgeneric and intrasubgeneric crosses were made with a view to find out phylogenetic relationship. The present results substantiate Burbidge's findings, wherein she has accomodated the species N. umbratica in the section suaveolentes of subgenus petunioides. The crossability and cytological studies revealed, that N. umbratica is closely related to N. megalosiphon (2n=40). The study also supports Good-speed's (1954) prediction that the further expansion of the genus above the 24 paired level is possible by amphiploidy. The fertile amphiploid N. megalosiphon-umbratica (2n=86) is a positive proof.
