Only one in five children with FAS has the physical signs of this condition such as a thin upper lip, small wide-set eyes, lower ears
and different creases in the hands.
Non-synchronization between silking and anthesis (Harris et al., 1976) and lack of photoassimilate during the grain filling period due to mutual shading (Bauman, 1960) may cause abortion of lower ears. In contrast to second-ear grain yield, increasing plant densities had a beneficial impact on top-ear grain yield (Table 2).
The other possible explanation was the effect of high plant density in the selection experiments for developing two-eared types resulting in a competitive disadvantage for prolific plants with lower ear height due to effects of shading.
This hierarchy is also exhibited among the axillary meristems, where upper ears dominate lower ears (Pinthus and Belcher, 1994).
When only grain bearing rows are counted at maturity (Tetio-Kagho and Gardner, 1988), results can be misleading if kernel abortion occurred along a complete row, as often occurs at lower ear positions.
At an individual plant level, this restriction is generally compensated by the production of kernels at lower ear positions (Fig.