Generally, orchids produce dust-like seeds in which endosperm reduction and embryo undifferentiation represent a derived state shared with species in about 11 other plant families. Orchid seeds are proposed to have a special kind of morphological or morphophysiological dormancy. We test this proposition, overcoming several design limitations of earlier studies, specifically that the in vitro germination method for orchid seeds uses pro-oxidants for disinfection and incorporates nitrate in the medium; both ‘treatments’ might contribute to dormancy breaking, potentially confounding judgement on the depth and nature of the dormant state. Seeds of the tropical orchid Dendrobium cruentum Rchb. f., were sown both in vitro, on a nutrient medium, and ex vitro, on plain agar omitting prior disinfection with sodium hypochlorite. Seeds previously stored and fresh seeds were incubated under combinations of vitro conditions, light treatments, constant or alternating temperatures and nitrate concentration. Seeds of D. cruentum are very small but have a large embryo that occupies most of the seed. Over a range of constant temperature seeds germinated to the spherical protocorm stage just as well ex vitro as in vitro. Neither light nor nitrate were prerequisites for ex vitro germination. The ability of D. cruentum seed to germinate in the absence of environmental or chemical stimuli suggests that mature seed can be non-dormant. Our results support the proposition that neither all DUST seed fit a dormancy class nor all orchids produce morphological or morphophysiological seeds. Finally, embryo/seed volume determinations in orchids may prove as valuable in studies on the evolution and ecology of germination and dormancy as embryo:seed ratios in other angiosperm species.

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兰花种子休眠概念：以石斛兰为模式物种

通常，兰花会产生类似灰尘的种子，其中胚乳减少和胚胎未分化代表与大约 11 个其他植物科的物种共享的派生状态。兰花种子被认为具有一种特殊的形态或形态生理休眠。我们测试了这个命题，克服了早期研究的几个设计局限性，特别是体外兰花种子发芽法采用促氧化剂消毒，培养基中加入硝酸盐；这两种“治疗”都可能有助于打破休眠，可能会混淆对休眠状态的深度和性质的判断。热带兰花的种子石斛RCHB。f., 都播种体外，在营养培养基上，和体外, 在普通琼脂上省略预先用次氯酸钠消毒。先前储存的种子和新鲜种子在体外条件、光处理、恒定或交替温度和硝酸盐浓度的组合下孵育。的种子D. cruentum非常小，但有一个占据大部分种子的大胚胎。在一定范围内的恒温种子也发芽到球形原球茎阶段体外作为体外. 光和硝酸盐都不是先决条件体外发芽。的能力D. cruentum种子在没有环境或化学刺激的情况下发芽表明成熟的种子可以是非休眠的。我们的结果支持这样的命题，即既不是所有 DUST 种子都适合休眠类，也不是所有兰花都产生形态学或形态生理学种子。最后，兰花的胚胎/种子体积测定在萌发和休眠的进化和生态学研究中可能被证明与其他被子植物物种的胚胎：种子比率一样有价值。