Developmental Anatomy of Tassel and Ear Shoots of Corn Grown with Different Levels of Boron

Abstract

1. Four weeks without boron was adequate to prevent differentiation of the staminate spike; in 6 or 8 weeks no spikelet primordia were formed, and the spikes were severely necrotic. After 4 weeks at 0.03 p.p.m. boron the cells showed no injury, and differentiation itself was more advanced than in the control. After 6 weeks, however, while the staminate spike continued to be more advanced than on normal plants, considerable injury was apparent in the upper spikelets. Eight weeks from the start of the treatment some pollen grains were formed, but many of these appeared abnormal because the contents were shriveled and had shrunken away from the wall. At the same time almost all pollen grains formed in the anthers of plants given 0.25 p.p.m. boron were normal. 2. Six weeks after treatment, ear buds had not yet begun growth. After 8 weeks pistillate spikes in the control plants were differentiating normal flowers. At 0.03 p.p.m. boron the spikes were almost as advanced as in the control plants, except that the growing tips of the lower pistillate flowers showed some injury. The spike from plants grown without boron was short with a few rudimentary spikelets; hypertrophy, hyperplasia, and necrosis were conspicuous. 3. Four weeks without followed by 6 weeks with boron, or 6 weeks without and 4 with, resulted in an abnormal staminate spike, but the pistillate spikes showed no apparent damage. Four weeks with and 6 weeks without boron, or 6 weeks with and 4 weeks without, resulted in both abnormal staminate and pistillate spikes. Boron in adequate quantity must be present at all times for growing corn in order to obtain normal kernel development.