Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Campus Fuentenueva, E-18071 Granada, Spain.
Langmuir. 2013 Jul 2;29(26):8370-6. doi: 10.1021/la4014202. Epub 2013 Jun 18.
Pearls, the most flawless and highly prized of them, are perhaps the most perfectly spherical macroscopic bodies in the biological world. How are they so round? Why are other pearls solids of revolution (off-round, drop, ringed pearl), and yet others have no symmetry (baroque pearls)? We observe that with a spherical pearl the growth fronts of nacre are spirals and target patterns distributed across its surface, and that this is true for a baroque pearl, too, but that in pearls with rotational symmetry spirals and target patterns are found only in the vicinity of the poles; elsewhere the growth fronts are arrayed in ratchet fashion around the equator. We argue that pearl rotation is a self-organized phenomenon caused and sustained by physical forces from the growth fronts, and that rotating pearls are an example--perhaps unique--of a natural ratchet.
珍珠，是其中最完美、最珍贵的一种，也许是生物界中最完美的球形宏观物体。它们为什么如此圆润？为什么其他珍珠是旋转体（不规则形状、水滴形、有环纹的珍珠），而另一些则没有对称性（异形珍珠）？我们观察到，球形珍珠的珍珠母生长前沿是螺旋形和靶形图案，分布在其表面，而对于巴洛克珍珠也是如此，但在具有旋转对称性的珍珠中，螺旋形和靶形图案仅出现在极点附近；在其他地方，生长前沿以棘轮方式排列在赤道周围。我们认为，珍珠的旋转是一种自组织现象，是由生长前沿的物理力引起和维持的，而旋转珍珠是自然棘轮的一个例子——也许是唯一的一个例子。
