Text 2 a. How Does a Tree Grow?

Trees grow in two ways. In a young shoot, bundles of cells form. As the shoot grows, a layer of cambium forms across and between the primary bundles where each year, cells in this layer divide and grow. As the cambium divides, wood and bark cells form. Cells pushed outward form the bark which eventually splits and falls off and is replaced. A tree’s upward growth occurs at the tip of each twig (figure 2.3).

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Figure 2.3 Tree growth

he inward growth of the cambium forms the main part of the trunk and is called xylem. Tiny tubes which transport water and minerals from the roots up the trunk and branches to the leaves make up the xylem. Leaves need this water to help them make food from sunlight. The outward growth is protected by a layer of phloem. The phloem is made up of tiny tubes that transport the sugars from the leaves to the rest of the tree. If the phloem is damaged the tree will die.

Roots may not go down deep but they can spread outward as far as the tree is tall. Roots anchor trees to the soil and absorb water and soil minerals needed for growth. Some trees have deep tap roots; others have a spreading system of roots. Roots as they push through the soil are aided by a cap that forms over the tender growing point of each root. Beyond this point, myriads of root hairs extend into the soil, increasing the surface area of the root and increasing the amount of water the tree can take up.

2.3 Find the answers to the following questions in the texts 1 and 2:

1. How can we determine the age of a tree?

2. What are false rings?

3. In what way do the leaves purify the air?

4. What is chlorophyll?

5. How do palm trees live without cambium?

2.4 Find sentences, showing the function of phloem in the texts1 and 2.

2.5 Explain using of the word “one” in the following sentences and translate them:

1. One must remember that the trees grow slower in cold weather.

2. The problem of reforestation is an important one.

3. We must meet one of these days.

2.6 Find sentences with the word “one” in the texts 1 and 2 and explain its using.

2.7 Skim the text 3. Write down an annotation of the text.

Text 3 Dendrochronology

Most trees can live 100 to 200 years, and some, like the giant redwoods and bristlecone pines, can live thousands of years.

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Figure 2.4 A cross-section of a tree

s trees age, they grow taller and wider. Each year, trees form new cells, which are arranged in rings around the tree’s center. So when you look at a cross-section of a tree, the rings you see will show you the amount of wood produced during one year. The study of tree rings is called dendrochronology.

Trees produce different amo­unts of wood in response to tem­perature, rainfall, and other condi­tions. Lots of rain increases tree growth, producing wider rings. Not enough rain or crowding from near­by trees both cause slower growth with narrow rings.

Dendochronologists are scientists who study past weather patterns by looking at tree rings. They can study trees in two ways. They look at cross-sections of dead trees that have fallen or been cut down (figure 2.4).Or they examine the inner wood of living trees without cutting them down by using special instruments that cut out a small sample from inside the tree.

The bristlecone pines in the White Mountains of California help dendochronologists learn how the Earth’s climate has changed over time. These trees are the oldest living organisms on Earth, providing as much as 5,000-year-long records of growth.