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Leaf-by-Leaf
13
Task Distribution
Aside from the impressive stature of some tree
trunks, leaves are certainly the most conspicu-
ous plant organs. And there's a reason for
this: While the pollination of blossoms, for
example, only takes up a limited portion of
a plant's life, the leaves are used through-
out the year. You already found out in the
chapter about plant cells (see page 14)
where the green color of the leaves comes
from and what a plant uses its chloroplasts
for. But the astonishing thing is that not
all cells of a leaf contain chloroplasts. Not
all cells have the same shape either. An inge-
nious division of work has been established in
the leaf in which each cell layer is assigned cer-
tain tasks.
Together We're Strong
The surface of a leaf is formed by a special cell layer — the epidermis. The most
conspicuous thing about the cells of the epidermis is that they don't contain any
chloroplasts. So it's not their job to absorb and convert sunlight. The epidermis is
specialized in protecting the inner workings of the leaf and preventing a lot of
water from evaporating from the leaf.
Both tasks of the epidermis are visible in the structure of the cells. If you look at
the epidermis from above, you will notice that its cells — which are different from
plant to plant — often have bizarre shapes. Little "arms" fit together like a puzzle.
Just like in a puzzle, the interconnected nature of the individual cells brings about
greater stability.
Cutting, Part 3 — Surface Sections
To observe the surface of a leaf under the microscope, you will need to pre-
pare a so-called surface section. This essentially involves slicing a thin piece of
the epidermis from the leaf surface. To do this, it's best to lay the leaf over a
curved surface, such as the bulb of the pipette or a thick marker, and hold it
with your thumb and index finger. Then place the razor blade flat onto the
leaf and cut a flat piece off. Here, too, the cut should be thin enough to pro-
duce a good microscopic image. Make sure you cut very lightly, as you do not
want to cut into the object below.
How many chloroplasts must there be in all of
the trees in a forest combined?
Dermal tissue with stomata
43
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