Stranglers and Buttresses
Some epiphytes eventually develop into stranglers. They grow long,thick roots that extend down the tree trunk into the ground. As they continueto grow, the roots form a sort of web structure all around the tree. At the sametime, the strangler plant's branches extend upward, spreading out into thecanopy. Eventually, the strangler may block so much light from above, andabsorb such a high percentage of nutrients from the ground below, that thehost tree dies.
Competition over nutrients is almost as intense as competition for light.The excessive rainfall rapidly dissolves nutrients in the soil, making itrelatively infertile except at the top layers. For this reason, rainforest treeroots grow outward to cover a wider area, rather than downward to lowerlevels. This makes rainforest trees somewhat unstable, since they don't havevery strong anchors in the ground. Some trees compensate for this bygrowing natural buttresses. These buttresses are basically tree trunks thatextend out from the side of the tree and down to the ground, giving the treeadditional support.
Rainforest trees are dependent on bacteria that are continually produc-ing nutrients in the ground. Rainforest bacteria and trees have a very close,symbiotic (共生的) relationship. The trees provide the bacteria with food,in the form of fallen leaves and other material, and the bacteria break thismaterial down into the nutrients that the trees need to survive.
One of the most remarkable things about rainforest plant life is itsdiversity. The temperate rainforests of the Pacific Northwest are mainly composed of a dozen or so tree species. A tropical rainforest, on the other hand, might have 300 distinct tree species. All Creatures, Great and Small
Rainforests are home to the majority of animal species in the world. And a great number of species who now live in other environments. 为适应我国高等教育发展的新形势,深化教育教学改革,提高教学质量,满足新时期**和社会对人才培养的新要求,教育部高等教育司于2004年1月颁布了指导高等院校大学英语课程教学的纲领性文件《大学英语课程教学要求(试行)》(以下简称《教学要求》)。作为大学英语教学改革一个组成部分,大学英语四、六级考试改革也正在稳步推进。这次大学英语四、六级考试改革的目的是更加全面地测量大学生英语综合应用能力,为新的《教学要求))的贯彻执行情况提供一个准确的评估依据,以适应我国大学英语课程教学的需要。
2004年在教育部高教司领导下,成立了大学英语四、六级考试改革项目组。该项目组和全国大学英语四、六级考试委员会(以下简称考试委员会)广泛听取了大学英语教师和学生的意见,经过反复研讨和论证,制定了四、六级考试改革方案。2005年6月四、六级考试开始采用新的计分体制和成绩报道方式,同年9月和2006年3月项目组和考试委员会分别公布了改革后四级和六级考试的样题,2006年6月和12月又分别进行了全国范围的四级和六级考试试点,并在此基础上完成了对大学英语四级和六级考试大纲的修订。
公布((大学英语六级考试大纲(2006修订版)》的目的是使广大师生了解改革后六级考试的考试目的、考试内容、考试形式、考核的语言技能与要求,以及新的成绩报道体系和分数解释。
在试卷构成上,对六级考试进行的改革主要体现在以下方面:
一、听力理解部分的分值比例从原来的20%,提高至35%;增加了长对话听力理解测试,复合式听写由原来的备选题型改为必考题型。
二、阅读理解部分增加了快速阅读技能测试。
三、词汇和语法知识不再单独列为考项,而融入了其他各部分试题中进行考核。
四、增加了句子层面的汉译英测试。