The only associations of solid stem and morphological characters concerned the hooded awns of Chinese Spring, as mentioned above, and the lax spike of S-615. As spike density is a genetically complex character, it does not help locate genes for solid stem.

These results support many previous reports that the D genome tends to make the culm of wheat hollow in that loss of any of the 3 D-genome chromosomes, XIX, XX and XXI, has resulted in a more nearly solid culm. Chromosome XX carries the gene O_D as identified by Yamashita (1937, 1947) and Matsumura (1952, 1953). Of its homoelogues II and XIII, II probably carries the gene m_A in the A genome and XIII has the gene for the hollow stem at locus M_B in the B genome.

This F₂ monosomic analysis of a quantitative character has shown that it is far more effective in locating genes in the monosomic parent than those in the variety that is tested against it. No genes in S-615 for solid stem have been located, probably because they are recessive. The proportion of disomic plants in a monosomic population is approximately one-fourth, the same as the proportion of homozygous recessives in a normal F₂ population. Monosomic lines of S-615 should reveal chromosomes critical for genes promoting solid stem.

(Excerpted from the author's draft by K. Y., Oct. 15, 1957)