Arrested development in the soybean field
Figure 7: Abscission probability of flowers/pods within a raceme. Picture is from Iowa State University. Abscission probability also varies among positions on a raceme. The ages of pods at position 1 (oldest) and position 5 (youngest) on the raceme in figure 7 differ by only 4 to 6 days. But, the sizes of the pods differ greatly. The pods at the first two positions are closer to the source of sugars and other nutrients. They are well nourished and dominate pods at other positions. Development of pods at position 4 and greater is often arrested so that they grow slowly or not at all. Under normal weather conditions, abscission probability is less than 5% for pods at positions 1 and 2 and 75% or greater for pods at position 4 and above (figure 7). Young pods located at upper positions on racemes develop into harvestable pods only if stresses damage pods at lower positions or caused them to abscise.