"As the tree grows from the outside," said Mr. Wilson, "the older part of the stem is subject to more and more pressure. The walls of soft matter between the wedges of wood become thinner and thinner, till they are the finest sheets, and the medullary tissue itself has ceased to be living matter. After this it no longer carries up the sap. When the stem is cut across, only the thin edges of these partition walls are seen, and they appear to be mere lines." "Thank you, sir," said Fred. "These are the lines then that the cabinet-maker calls the silver-grain of the wood.""Yes, Fred, they are," said Mr. Wilson. "The beauty ofthe wood depends upon the closeness of its texture, and the skill of the workman in cutting it so as to expose this silver grain. Which part of the woody stem did you say was first formed?""The central part of the stem, sir, is the oldest wood in the tree.""Tell me again what happens to this part as new layers are formed one by one around it?""The outer layers press upon it more and more, sir, and it becomes denser and denser.""Quite true," said Mr. Wilson, "and it becomes the hardest wood in the tree. It is called heartwood. Heart- wood is always selected where strength and durability are required. The heartwood becomes darker and moredeeply coloured than the layers round it, and it is the graduation of coloring that makes our cabinet woods so beautiful.
同类推荐
语文新课标课外必读第一辑——格兰特船长的儿女
国家教育部颁布了最新《语文课程标准》,统称新课标,对中、小学语文教学指定了阅读书目,对阅读的数量、内容、质量以及速度都提出了明确的要求,这对于提高学生的阅读能力,培养语文素养,陶冶情操,促进学生终身学习和终身可持续发展,对于提高广大人民的文学素养具有极大的意义。语文新课标课外读物——海底两万里
现代中、小学生不能只局限于校园和课本,应该广开视野,广长见识,广泛了解博大的世界和社会,不断增加丰富的现代社会知识和世界信息,才有所精神准备,才能迅速地长大,将来才能够自由地翱翔于世界蓝天。否则,我们将永远是妈妈怀抱中的乖宝宝,将永远是温室里面的豆芽菜,那么,我们将怎样走向社会、走向世界呢?学生语言文字写作学习手册—教你学同义词反义词(下)
语言文字的简称就是语文。语文是人文社会科学的一门重要学科,是人们相互交流思想的工具。它既是语言文字规范的实用工具,又是文化艺术,同时也是用来积累和开拓精神财富的一门学问。教育创新与应用型创新人才培养
本书基于浙江万里学院应用型创新人才的探索与实践,从致力于教育创新到培育应用型创新人才,分为“教育创新篇”和“应用型创新人才培养篇”。“教育创新篇”,集成了浙江万里学院十年教育创新和教学改革之精华,是本书的核心和主体。“以能力为核心,创新高素质应用型人才培养模式”所提出的“面向社会,一核心、双符合、三体系、四途径”的高素质应用型人才培养模式,为应用型创新人才培养提供了思路,树立了范本。
热门推荐