Plant Biomechanics Group, Botanic Garden, University of Freiburg, Freiburg im Breisgau, Germany.
Freiburg Materials Research Center (FMF), University of Freiburg, Freiburg im Breisgau, Germany.
J R Soc Interface. 2019 Aug 30;16(157):20190327. doi: 10.1098/rsif.2019.0327. Epub 2019 Aug 7.
The fruits of Chinese witch-hazel (Hamamelis mollis, Hamamelidaceae) act as 'drying squeeze catapults', shooting their seeds several metres away. During desiccation, the exocarp shrinks and splits open, and subsequent endocarp deformation is a complex three-dimensional shape change, including formation of dehiscence lines, opening of the apical part and formation of a constriction at the middle part. Owing to the constriction forming, mechanical pressure is increasingly applied on the seed until ejection. We describe a structural latch system consisting of connective cellular structures between endocarp and seed, which break with a distinct cracking sound upon ejection. A maximum seed velocity of 12.3 m s, maximum launch acceleration of 19 853 m s (approx. 2000g) and maximum seed rotational velocity of 25 714 min were measured. We argue that miniscule morphological differences between the inner endocarp surface and seed, which features a notable ridge, are responsible for putting spin on the seed. This hypothesis is further corroborated by the observation that there is no preferential seed rotation direction among fruits. Our findings show that H. mollis has evolved similar mechanisms for stabilizing a 'shot out' seed as humans use for stabilizing rifle bullets and are discussed in an ecological (dispersal biology), biomechanical (seed ballistics) and functional-morphological (fine-tuning and morphospace of functional endocarps) contexts, and promising additional aspects for future studies are proposed.
中国金缕梅（Hamamelis mollis，金缕梅科）的果实充当“干燥挤压弹射器”，将其种子弹射到几米之外。在干燥过程中，外果皮收缩并裂开，随后内果皮的变形是一个复杂的三维形状变化，包括裂缝线的形成、顶端部分的打开和中部形成收缩。由于形成了收缩，机械压力逐渐施加在种子上，直到弹射出去。我们描述了一个由内果皮和种子之间的连接细胞结构组成的结构闩锁系统，在弹射时会发出明显的破裂声。测量到的最大种子速度为 12.3 m s，最大发射加速度为 19 853 m s（约 2000g），最大种子旋转速度为 25 714 min。我们认为，内果皮表面和种子之间的微小形态差异是导致种子旋转的原因，种子内表面有一个明显的脊。这一假设进一步得到了观察结果的证实，即果实之间没有种子优先旋转方向。我们的研究结果表明，H. mollis 已经进化出了类似的机制来稳定“射出”的种子，就像人类用于稳定步枪子弹一样，我们从生态（传播生物学）、生物力学（种子弹道学）和功能形态学（精细调整和功能内果皮的形态空间）等方面进行了讨论，并提出了未来研究的其他有前景的方面。
