3. Gametophyte factor in chromosome 3. A gametophyte factor which has a deleterious effect on the functioning of the male gametophyte has been studied in some detail. The following conclusions have been reached from a large amount of data:
1. The linear order is ga et A lg2 with ga about 6 units from et. (et is about 10 units from A.)
2. The percentage of functioning ga pollen, when equal amounts of Ga and ga pollen are present, varies from 2‑8%. There is some, though slight, influence of the maternal silk constitution on the percentage ga pollen which achieves fertilization.
3. There is no effect of ga on the female gametophyte and plants homozygous for ga have been obtained.
4. Some interesting data were obtained from plants heterozygous for ga and a‑x2. a‑x2 is an "allele" of A found by Stadler in his X ray studies; it probably is a deficiency. a‑x2 pollen does not function as well as normal pollen but the extent is variable. There is a slight but significant elimination of a‑x2 eggs. Crossing over is also reduced with a‑x2 to approximately half the standard value for the et‑A region. Pollen from plants of ga A/Ga a‑x2 constitution consists chiefly of the two noncrossover classes (ga A and Ga a‑x2). Crossovers give rise to Ga A and ga a‑x2 pollen. The ga a‑x2 pollen grains carry two harmful loci and never achieve fertilization. The other crossover class, Ga A, has a marked advantage over either of the two parental types. If only A seeds are analyzed from the cross of a a x ga A/Ga a‑x2 it is found that a great majority of them (82%) are due to the functioning of Ga A pollen; i.e., there is a great excess of the crossover class. Ga a‑x2 pollen grains have a striking advantage over ga A pollen but considerable variation was found in the frequency with which the two types functioned. When ga A/Ga a‑x2 plants are selfed about 30% of the zygotes should be homozygous for a‑x2. The abortion of these should lead to sterility on the ear. Surprisingly enough in the few ears so far obtained of this kind very little sterility has occurred. It is possible that we are dealing here with a case of selective fertilization; i.e., the a‑x2 embryo sac rejects pollen tubes of the same constitution and only or chiefly accepts sperm of Ga A or ga A constitution.