| Talk about an old-growth forest. Newly described fossils push back the appearance of wood by at least 10 million years. The fossils, including one from 407-million-years-old rocks in France, preserve the remains of stems about 12 centimeters long. The size and arrangement of cells in the cores of the stems, and particularly the presence of long, thin cells (arrows) that span several rings of cells and extend like rays from the center toward the outer rims, are characteristic of wood, researchers report online today in Science. The plants' small size, as well as the presence of thick-walled cells elsewhere in the stems, suggests that wood evolved to efficiently transport water from the soil into the plant. At the time these plants lived, atmospheric concentrations of carbon dioxide were decreasing, which in turn decreased the water-use efficiency of the plants and boosted their need for water, the scientists say. Although the first plants sporting wood were small, subsequent species quickly took advantage of wood's structural strength: In just a few million years, some had attained treelike stature. |
谈谈古老的森林。新发现的化石将木材的出现提前了至少1000万年。这些化石中的一块来自四亿零七百万年前的法国岩石，保留的主干残骸长约为12厘米。研究人员今天在《科学》杂志在线版上报道说：树干芯部的细胞大小和排列具有木材的特点，特别是那些细长的细胞（箭头所指方向），跨越了好几个细胞圈延伸出去，就像光线从中心射向外围一样。这种植物矮小，主干别处存在厚壁细胞，说明这种木材在生长过程中可以高效地把水从土壤中传输到植物上。科学家们说，这些植物生存的时候，大气中的二氧化碳浓度正在降低，这样反而降低了这种植物的对水的利用效率，引起了缺水。尽管这种最初的植物长出的木材矮小，后来的品种很快吸收了木材结构的优点，在仅仅几百万年的时间里，一些植物就拥有了类似于树的主干。 |
