الأربعاء، 9 أبريل 2014

موضوع انشائي باللغة الانجليزية عن ساق النبات Plant stem

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, flowers, cones or other stems etc. The other main structural axis of plants is the root. In most plants, stems are above the soil surface but some plants have underground stems called stolons or rhizomes.

Stems have four main functions which are:[1]

Support for leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.
Transport of fluids between the roots and the upper parts in the xylem and phloem.
Storage of nutrients.
The production of new living tissue. Stems have tissue called the meristem which contains dividing cells. This produces new living tissue each year.
The normal life span of plant cells is one to three years. Much of the longer-lasting tissue in trees consists of cells which are no longer living. Bark and xylem vessels are examples of this.

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