DORMANCY IN SEEDS OF HIBBERTIA-CUNEIFORMIS AND H-HUEGELII (DILLENIACEAE)

Dormancy delays the germination of seeds in two species of the primiti ve angiosperm genus Hibbertia (H. cuneiformis and H. huegelii, family Dilleniaceae). After seed coat removal, germination increased in 18-mo nth-old seeds of H. cuneiformis and 6- to 8-month-old seeds of H. hueg elii. Hence, seeds of the two species exhibit seed coat dormancy. The removal of the seed coat may stimulate germination, as the result of i ncreased water uptake, and/or the removal of mechanical and chemical i nhibition. However, the occurrence of imbibitional injury and a reduce d percentage of vigorous seedlings in decoated seeds suggest that embr yo dormancy, as a second type of dormancy, impedes germination in N. c uneiformis. Embryo dormancy also delays the germination of seeds of H. huegelii, since a high percentage of seeds did not germinate after re moval of the seed coat. Embryo dormancy appears to vary among individu al seeds and between species. The germination experiments suggest a hi gh percentage of non-dormant and weakly dormant embryos for 18-month-o ld seeds of H. cuneiformis. By contrast, many seeds of H. huegelii app ear to contain deeply dormant embryos.:In H. cuneiformis, the depth of the seed dormancy varied with the age of the seeds. Freshly harvested seeds did not germinate for 3 months. Treatment with gibberellic acid (GA(3)) (120 mg L-1) significantly enhanced germination of freshly ha rvested and 18-month-old, intact seeds of H. cuneiformis and the germi nation of decoated 18-month-old seeds of H. huegelii. The plant hormon es kinetin and abscisic acid did not affect the final germination perc entage in 18-month-old seeds of N. cuneiformis. For H. huegelii, germi nation was reduced in decoated seeds and seeds with cracked coats expo sed to an 8 h day:16 h night diurnal cycle compared with complete dark ness.