4. Further studies with plants hyperploid for the short arm of chrom. 5 show that secondary trisomes, involving the fragment chrom., are found in the progeny of hyperploid individuals. The breeding behavior of the fragment of hyperploid plants is as follows:
|Type of offspring in %||
|2N + fragment||29.7%||0.6%|
The above data show that the fragment chrom. is readily transmissable through the female side but only rarely do male gametophytes hyperploid for the fragment chrom. function. The frequency of secondaries, however, through the male side is as great, at least, as through the female side. Pollen from secondary trisomes gave only disomic offspring in the limited backcross tests made which indicates that pollen hyperploid for the "secondary" chrom. can not successfully compete with haploid grains. Among the questions to be answered are (1) How do the secondaries arise and (2) How do those male gametophytes from fragment plants which bring in the "secondary" chrom. manage to successfully compete with haploid pollen when pollen hyperploid for the fragment chrom. is rarely successful.