Kordesii Roses [ Tetraploid ]A hybrid between R. rugosa and R. wichuraiana named Max Graf (I 9 I 9) was a sterile diploid, but Kordes succeeded in raising three seedlings from it in 1940 and 1950-1 which were fertile tetraploids, the beginning of a new race of Kordesii hybrids, such as Parkdirektor Riggers. This rose is a conversion from a diploid to a tetraploid.