Development of seed coat-imposed dormancy during seed maturation in Cynoglossum officinale. -Physiol Plant, 97: 28-34,The relationship between seed phenolics and appearance of seed coat-imposed dormancy during seed development in Cynoglossum officinale L, was studied. Up to 24 days after anthesis, seeds failed to genninate upon imbibition in Petri dishes at 25°G, At 44 days after anthesis, seeds were fully geiminable; removal of seed coats did not improve their germination or O2 uptake. At 72 days after anthesis. mature seeds at the base of the cyme did not germinate unless their coats were removed. Removal of seed coat also stimulated O2 uptake at this harvest date. The methanol-soluble phenolic content of the seeds increased during the early stages of seed development, in both the seed coat and the embryo. As seed development continued, the methanol-soluble phenolic content of the embtyo stabilized, but that of the seed coat declined. This decline was associated with an increase in the thioglycohc acid-soluble phenolics, presumably lignins, in the seed coat. These results suggest that polymerization of methanol-soluble phenolics into lignins in the seed coat during later stages of seed development renders the seed coat of C. officinale impermeable to Oj, and thus keeps the seed dormant.