The Development of Ear Prirnordia of Zea In Relation to Position on the Plant

The development of auxiliary buds of a yellow dent maize hybrid was studied. Seven buds at acropetally successive nodes survived at least to 68 days after planting and became pistillate inflorescences, potential ears. Meiosis occurred in the basal ovaries of the upper two ears after 68 days, when the styles were 2 mm. long, and complete embryo sacs were present by 71 days. The two upper ears attained approximately the same morphological and cytological stage between 68 and 71 days. The top bud invariably became the harvestable ear. The failure of complete development of the second ear is not ascribed to inadequate ovule development by the time of anthesis, nor to failure of pollination of this ear, but to factors associated with competition prior to, and after anthesis. 13. A comparison of the mode-The time required for floral abscission in Lizard\u27s Tail variety is less and more uniform than in Little Turkish. Factors which affect abscission in general and which cause a varying effect in the two varieties include auxin concentration, leaves (sources of carbohydrates), methyl donors, and pectic enzymes. Concentrations of 100 ppm, 1,000 ppm, and 10,000 ppm IAA are more effective in retarding abscission in Little Turkish variety; low concentrations (5 ppm) tend to accelerate abscission slightly in Little Turkish and retard the process in Lizard\u27s Tail. It is suggested that carbohydrate levels are higher in Little Turkish and have a varying effect upon abscission in the two varieties. A lack of a methyl donor is more limiting in Little Turkish. Addition of 0.01 percent methionine resulted in a 32 percent decrease in time of abscission in Little Turkish and a 19 percent decrease in Lizard\u27s Tail. Response to higher concentrations is much the same in both varieties. Pectin-methylesterase activity is higher in Little Turkish, and since this enzyme prevents abscission, its greater abundance aids in explaining differences between the two varieties. The results indicate that abscission is controlled by the interaction of many factors and that a variation in the concentration, activation, or transport of any one or any combination affects the mode of abscission generally