It is interesting to know Popular poplars

Growing in most of the eastern USA and now blooming with showy flowers is one of the tallest and most beautiful of eastern hardwood trees: the yellow poplar. Its wood is used for furniture, crates, musical instru­ments and pulpwood. Its flowers give the tree its nicknames of tulip-poplar and tulip-tree (figure 1.5). Standing upright at the ends of leafy twigs are

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Figure 1.5 Tulip-tree branch with a flower

he two-inch tall cup-shaped flowers that resemble tulips. They’ve six rounded green petals that are orange at the base. The flowers mature into tan cone-like fruits composed of many overlapping bullets, that shed from the still-upright fruit in fall. Another identifying feature of the tulip-tree is its squarish leaves with broad tips and straight bases, besides the leaf looks like the capital letter T.T. for tulip-tree.

Interesting facts about trees

Figure 1.6 Tree trunk covered in spikes

• Only plants produce enough new oxygen to support life on Earth. In one year, an average tree inhales 12 kilograms (26 pounds) of CO₂ and exhales enough O₂ to keep a family of four breathing for a year.

• Trees can do some pretty interesting things to survive. For example, the baobab lives in tree that parts of Africa, where it is hot and dry for long periods, stores water in its thick trunk during the rainy season. When the rains have stopped and it is hot and dry again the trunk shrinks as the tree uses up the stored water.

• Some trees are even covered with spikes for protection, like this tree species in Honduras (figure1.6).

4.10 Topic for discussion.

Do you know any interesting facts about trees?

Unit 2 How trees live and grow

2.1 Active vocabulary

coloring matter	красящее вещество
decay	гнить
false ring	ложное годичное кольцо
lumber	древесина
missing ring	пропущенное годичное кольцо
outer edge	внешняя кромка

partial ring	частичное годичное кольцо
shoot	росток, побег
starch	крахмал
terminal bud	верхушечная почка
woody fiber	древесное волокно

2.2 Read and translate the text1 using a dictionary. Text 1 How Trees Live

A tree has three main parts. The roots anchor it in the ground. They absorb water and dissolve minerals. The trunk and branches carry sap and hold the leaves in the sunlight. The leaves make food. A tree grows higher and wider as its twigs and branches lengthen at the tips. Meanwhile the branches, twigs, and trunk grow thicker. Conifers and most deciduous trees add thickness.

Figure 2.1 This basswood trunk cross section has 24 distinct annual rings

Every year the cambium adds a layer of new cells to the older wood. Each layer forms a ring. By counting the rings one can tell the age of the tree (figure 2.1). They are thick in years of good rainfall and thin in poor years.

There may, however, be false rings, caused by interruptions of the water supply in the growing season. Drought, frost, fire, or disease may cause false or partial rings. A dry year may also result in a missing ring. A true annual ring can be identified by its sharp outer edge; a false ring, by its fuzzy border.

Water and minerals travel up from the roots to the leaves in the new layers of wood inside the cambium. Hence this part of the trunk is called sapwood (or xylem). Other sap carries food down from the leaves through a layer called phloem inside the bark.

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Figure 2.2 A cross-section of a palm tree

alm trees have no cambium. The woody fibers in the pithy mass of the trunk carry sap up and down. The trunk grows only at the top from a terminal bud. As the tree grows, the older sapwood stiffens with a hard material (lignin) and loses connection with the leaves.

Then it just stores water. At last it becomes solid heartwood. Heartwood makes the best lumber. If it decays, a tree surgeon can replace it just as a dentist fills a decayed tooth. A tree’s roots grow at the tips like branches and twigs. Many trees send a main taproot straight down. It may grow to a great depth seeking water.

While the cambium makes the tree trunk and its branches grow in size, the leaves produce the food that builds the tissues of the tree. Using the energy from sunlight, the green coloring matter in the leaves (chlorophyll) takes carbon dioxide out of the air. It combines the carbon dioxide with water and dissolved minerals from the roots to form sugars and starches. One cannot see the food-making process at work, but one can feel a result of it in the woods on a hot summer day. In the shade, the air is cool and fresh. The leaves cut off the glare of the sun and reduce heat by breathing out tons of water vapor into the air. This water was soaked up by the roots and carried to the leaves through the sapwood. The water not used in making food is breathed out into the air through pores in the leaf. Moreover, leaves purify the air by taking out carbon dioxide and giving back oxygen.