School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506-0225 USA.
Am J Bot. 2001 Aug;88(8):1444-51.
Fruits (drupes) of Symphoricarpos orbiculatus ripen in autumn and are dispersed from autumn to spring. Seeds (true seed plus fibrous endocarp) are dormant at maturity, and they have a small, linear embryo that is underdeveloped. In contrast to previous reports, the endocarp and seed coat of S. orbiculatus are permeable to water; thus, seeds do not have physical dormancy. No fresh seeds germinated during 2 wk of incubation over a 15°/6°-35°/20°C range of thermoperiods in light (14-h photoperiod); gibberellic acid and warm or cold stratification alone did not overcome dormancy. One hundred percent of the seeds incubated in a simulated summer → autumn → winter → spring sequence of temperature regimes germinated, whereas none of those subjected to a winter → spring sequence did so. That is, cold stratification is effective in breaking dormancy only after seeds first are exposed to a period of warm temperatures. Likewise, embryos grew at cold temperatures only after seeds were exposed to warm temperatures. Thus, the seeds of S. orbiculatus have nondeep complex morphophysiological dormancy. As a result of dispersal phenology and dormancy-breaking requirements, in nature most seeds that germinate do so the second spring following maturity; a low to moderate percentage of the seeds may germinate the third spring. Seeds can germinate to high percentages under Quercus leaf litter and while buried in soil; they have little or no potential to form a long-lived soil seed bank.
平枝荀子的果实（核果）在秋季成熟，并从秋季到春季传播。种子（真正的种子加上纤维状内果皮）在成熟时处于休眠状态，并且它们具有发育不良的小线性胚。与之前的报道相反，平枝荀子的内果皮和种皮对水是可渗透的；因此，种子没有物理休眠。在 15°C/6°C-35°C/20°C 的温度范围内，在光照（14 小时光周期）下培养 2 周，没有新鲜种子发芽；赤霉素和温暖或寒冷分层本身都不能克服休眠。在模拟的夏季→秋季→冬季→春季温度条件下，100%的种子发芽，而在冬季→春季序列下，没有种子发芽。也就是说，只有在种子首先暴露于温暖温度期之后，冷层积才有效地打破休眠。同样，只有在种子暴露于温暖温度之后，胚胎才在冷温度下生长。因此，平枝荀子的种子具有非深复杂的形态生理休眠。由于散布物候和休眠解除的要求，在自然界中，大多数在成熟后第二年春天发芽的种子；有少量种子可能在第三年春天发芽。在栎树叶层和土壤中埋藏时，种子可以以较高的百分比发芽；它们形成长期土壤种子库的潜力很小或没有。
