Département de Géologie, Université de Liège (U.Lg), B18 Sart Tilman, B-4000 Liège 1, Belgium.
Science. 2011 Aug 12;333(6044):837. doi: 10.1126/science.1208882.
The advent of wood (secondary xylem) is a major event of the Paleozoic Era, facilitating the evolution of large perennial plants. The first steps of wood evolution are unknown. We describe two small Early Devonian (407 to 397 million years ago) plants with secondary xylem including simple rays. Their wood currently represents the earliest evidence of secondary growth in plants. The small size of the plants and the presence of thick-walled cortical cells confirm that wood early evolution was driven by hydraulic constraints rather than by the necessity of mechanical support for increasing height. The plants described here are most probably precursors of lignophytes.
木质部（次生木质部）的出现是古生代的一个重大事件，促进了大型多年生植物的进化。木质部进化的最初步骤尚不清楚。我们描述了两种具有次生木质部的小型早泥盆世（4.07 亿至 3.97 亿年前）植物，其中包括简单射线。它们的木材目前代表了植物中次生生长的最早证据。植物的体型较小，以及厚壁皮层细胞的存在，证实了木质部的早期进化是由水力限制驱动的，而不是为了增加高度的机械支撑的必要性。这里描述的植物很可能是木质植物的先驱。
