Abstract
Seeds with physical dormancy have a water-impermeable seed coat or fruit coat (endocarp), and
thus scarifying the hard coat improves germination. The purpose of the present study was to use water
uptake as a criterion to determine if the seed / fruit has physical dormancy, and to use dye-tracking
to identify the water gap and impermeable layers of the seed/fruit coat in 3 species of woody plants
native to Taiwan. The seed plus endocarp (hereafter referred to as the seed) of Rhus succedanea
(Anacardiaceae), and seeds of Thespesia populnea (Malvaceae), and Colubrina asiatica (Rhamnaceae)
exhibited physical dormancy. The water gap of R. succedanea seeds was located on the micropylar
end of the seed and was a narrow-linear opening. The endocarp had 3 water-impermeable layers,
with macrosclereids on the outside, palisade sclereid cells in the middle, and serrulate sclereids
on the inside, the latter reported for the first time in plant seeds. The water gap of T. populnea seeds
was located on the end opposite the micropyle and was a chalazal plug surrounded by a layer of palisade
sclereid cells in the seed coat, and water passed through the slit between the plug and sclereid
cells. The water gap of C. asiatica seeds was located on the micropylar end of the seed and was a
narrow-linear opening, and the seed had a water-impermeable layer of palisade sclereid cells. High
percentages of fresh seeds mechanically scarified at the water gap spot of the 3 species germinated.
Immersion of seeds in hot water and allowing them to cool in the water also increased germination
percentages, and the optimal water temperatures were 70℃ for seeds of R. succedanea and 80℃ for
those of T. populnea and C. asiatica. Concentrated sulfuric acid broke dormancy in R. succedanea
seeds, and the soaking time for the highest germination percentage was 90 min. The optimal
temperatures for germination of R. succedanea seeds was 20/10 and 25/15℃, and those for T. populnea and C.asiatica seeds were 30℃ and 30 / 20℃, respectively.