Leaves are very important to trees, because trees use their

      leaves to make their food. When trees are hungry–and they're

      always hungry–they just hold their leaves up to the light.

      LEAVES

      MIX

      WATER

      WITH

      CERTAIN

      PARTS of the air to

      make

      sugar. To do that, they need energy, and they get this

      energy from light.

      Wait a minute. Leaves use air? Does this mean

      they can breathe just like you?

      Yes,

      leaves breathe in

      and out—through their mouths, which they can open

      and shut. These mouths even have

      lips,

      just like yours.

      But there is one big difference.

      A tree doesn't have just

      one mouth

      —

      it has

      thousands. They're

      all very tiny, and

      they're located on

      the undersides of

      the leaves. When

      it's very hot and

      dry, trees close their

      mouths because they

      lose lots of water

      when they breathe,

      just like you do. (You

      can see this if you breathe on a windowpane—the

      moisture from your breath will fog the glass.)

      Larches ace one

      of

      just three conifers that turn yellow

      in the fall and shed their needles

      for

      the winter.

      *

      If you

      close your mouth, you won't suffocate, because

      you can still breathe through your nose. When it's dry

      outside and a tree shuts its many mouths, it doesn't

      suffocate either, because it can still take in air through

      its bark and roots,

      The upper surface of

      the

      leaves has

      a

      waxy coating,

      which often makes them shiny. The sun shines on the

      tops of the leaves, and because the leaves are so

      thin,

      they can easily dry out. The wax makes them

      thicker so they can hold in moisture, and this keeps

      them healthy.

      The leaves of each species of tree look different.

      Hornbeam leaves, for example, have notched edges

      like a saw. Others—such as oak leaves—have wavy

      edges.

      There's also a big difference between deciduous

      trees and conifers. Deciduous trees have big, flat

      leaves, The leaves of conifers are narrow and pointed,

      like needles—and they

      can

      prick

      you.

      This is how coni-

      fers protect themselves so that deer won't eat them.

      In the winter, deciduous trees drop their leaves,

      but conifers hold onto their needles. They do this

      because many of them live where it's very

      cold.

      The

      winters are long and the summers are very short. So

      it's better for the trees to stay green the whole time,

      That way they can start to make sugar whenever a

      warm day arrives. If they had to wait to grow new

      leaves first, summer would be over before they had

      time to make any

      food.

      Flat leaves are very sensitive, and they really don't

      like cold weather. The leaves of deciduous trees such

      as oak and beech would freeze on the first frosty day.

      That's why these trees drop their leaves before winter.

      The needles of spruce trees and other conifers contain

      oil that protects them from freezing.

      *

      But there are a few conifers that behave like decidu-

      ous trees: the larch, the dawn redwood, and the bald

      cypress. In the

      fall,

      their needles turn yellow and fall

      off. That's why a lot of people think these trees are

      dead when they see them in winter.

      Really, they're just sleeping

      through the cold time

      of year.

      TREES

      LIVE

      IN

      MANY

      DIFFERENT

      environments–

      dry or wet. hot or cold–ond the shape and

      size of their leaves

      is

      important.

      In

      tropical rain

      forests, large leaves with pointed tips shed

      water