Fire stimulates the germination of most seeds in fire-prone vegetation. Fruits of Leucadendron (Proteaceae) are winged achenes or nutlets that correlate with their requirements for smoke and/or heat in promoting germination. We describe five possible smoke–heat dormancy-release/germination syndromes among plants, of which Leucadendron displays three (no response, smoke only, smoke and heat). As seed-coat thickness varies with seed-storage location (plant or soil) and morphology (winged or wingless), we tested its possible role in water uptake and germination. Species with winged seeds achieved 100% germination in the absence of smoke/heat, seed coats were an order of magnitude thinner, and their permeability greatly exceeded that of nutlets. As seed-coat thickness increased (1) imbibitional water uptake declined at a decreasing rate, and (2) the response to smoke, and to a lesser extent heat, increased linearly to reach levels of germination approaching those of winged seeds. For species responsive to smoke and heat, there was no additive effect when applied together, suggesting that they may have promoted the same physiological process. We conclude that seed-coat thickness holds the key to germination requirements in this genus, independent of seed-storage location or morphology. By what mechanisms (1) the smoke response is greater the thicker the seed coat and (2) smoke chemicals might increase water permeability to explain the non-additive effect of smoke and heat, warrant further investigation.

火刺激了易发火的植被中大多数种子的发芽。Leucadendron (Proteaceae) 的果实是带翅的瘦果或小坚果，它们与促进发芽所需的烟雾和/或热量相关。我们描述了植物中五种可能的烟热休眠释放/发芽综合征，其中Leucadendron显示三个（无响应、仅烟雾、烟雾和热量）。由于种皮厚度随种子储存位置（植物或土壤）和形态（有翅或无翅）而变化，我们测试了它在吸水和发芽中的可能作用。有翅种子的物种在没有烟/热的情况下实现了 100% 的发芽，种皮薄了一个数量级，并且它们的渗透性大大超过了小坚果。随着种皮厚度的增加（1）吸水量以递减的速度下降，（2）对烟雾的反应，以及在较小程度上的热量，线性增加，达到接近有翅种子的发芽水平。对于对烟和热有反应的物种，一起使用时没有叠加效应，这表明它们可能促进了相同的生理过程。我们得出结论，种皮厚度是该属发芽要求的关键，与种子储存位置或形态无关。通过什么机制（1）烟雾响应越大，种皮越厚，（2）烟雾化学物质可能会增加水的渗透性，以解释烟雾和热量的非累加效应，值得进一步研究。