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EXAMINING STEMS AND LEAVES

One of the jobs that a leaf has to do is to protect the stem
from the hot sun. Did you know that stems can actually get
sunburned, just like we can? The leaves offer some shade to
the stems, and they grow out from the stem in the best way to
protect the stem of the particular plant on which they grow.

There is a pattern in the ways that leaves grow from stems.
Plants that are the same will have the same pattern, because
they reproduce their own kind. Each kind of plant has its
own pattern. Yet, they all have some of the same
characteristics, and that pattern is the one we will study
now. We'll take a little walk around the schoolyard, and
examine the different plants. We can do the same thing
later, at home, by examining plants in our own yards and the
yards of our neighbors.

The leaves of grasses (called "blades") grow right out of the
stem. Most leaves of other plants are attached to the stem
by a little stalk (tiny stem) called a "petiole" (pronounced
"pet-tee-ol"). At the base of the petiole on some plants,
there are two tiny leaf-like things that stick out, called
"stipules" (pronounced "stip-yules"). Most plants don't have
stipules.

The swollen places on stems are called "nodes," and this is
where leaves grow. On some plants, there will be only one
leaf at each node. Then, there will be a pattern in which
the nodes (or leaves) will take turns being on different
sides of the stem. Some will grow toward the sun, and some
will grow toward the ground. If you look at each leaf or
node, and count them, you will see that #1 is toward the sun,
#2 is to the side. #3 is to the ground, and #4 is growing to
the other side. The next #1 will be in the same position as
the first # 1. Some will grow toward the sun and others will
grow toward the ground. This is called a "spiral pattern."
How many plants can you find with their leaves growing in
this same kind of spiral pattern?

On other plants, there will be two leaves growing from each
node. They will have leaves growing out on only two sides of
the stem, and they will be on opposite sides. The leaves
will not grow out from the top side and bottom side of the
stem, but will turn to face the sun, and unless you look
closely at the stem, you will think all the leaves grew out
from the top of the stem. See how many different plants you
can find with this opposite pattern, and put them on your
list.

I just looked at the new growth on my hackberry tree. It has
nodes on all sides of the stem, in a spiral pattern. From
each node, there grew one petiole with a leaf, and another
little stalk with three tiny stalks growing out from its
terminal bud. The three tiny stalks each have one very tiny
flower on the ends. Those flowers will grow into black-
colored berries. The birds will enjoy most of those berries
next winter, and some of the berries will start new trees,
because they are the tree's seeds.

Some stems have more than two leaves growing out from their
nodes. These leaves are whorled, which means that the edge
of one leaf is on top of, and at the center of the leaf that
came before it. Kind of the way playing cards are "whorled"
in your hand when you hold several at one time.

There are a few plants which have more than one pattern of
leaf growth. See if you can find one. You could be a leaf-
pattern detective! That would be fun!


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