Thames & Kosmos TK2 Scope, Experiment Manual

Did You Know?

The Fine Art of Leaf-Cutting

In order to gain an overview of all of the tissues in a leaf, it’s best to make a 
cross-section through it. You will need:

• a slide and a cover slip
• the pipette and water
• a razor blade (see page 11)
• the tweezers
• various leaves, preferably thicker ones such as those of a boxwood, ficus, ivy, 
or even an evergreen tree
• styrofoam or a piece of carrot

As easy as preparing a cross-section of a leaf may sound, unfortunately it is 
usually rather difficult. Use the same procedural principles as those you fol-
lowed on page 38. First cut a slit into the styrofoam and stick the leaf into it. 
You can also use a piece of carrot for this purpose. Then cut a layer off with 
styrofoam and all. That way, the leaf and the styrofoam are in one plane. Now 
place the razor blade on the styrofoam and cut the leaf and styrofoam as 
thinly as possible. Go ahead and make 10 or 15 cuts like this while you’re at it. 
This will greatly increase the chances of their being a sufficiently thin section 
among them.

The problem with preparing leaf cross-sections is that many leaves are very 
thin and soft and are consequently also very difficult to cut. It’s best to use 
somewhat thicker or tougher leaves for practice at the beginning — such as 
boxwood or ivy — before moving on to more tender objects. But sometimes 
it is very difficult to get good, clean cross-sections. Leaves that are too thick 
have the unpleasant tendency of folding over when cut, so that what you’re 
looking at is not the cross-section but a top view of the top or underside of the 
leaf. So here’s another tip: Cut very thin wedges. You surely won’t be able to 
see anything on the thick end, but you will generally get a good cross-section 
on the thin end. Apart from that, the rule is: Practice makes perfect!

In leaf cross-sections, one finds many round or oval cell groups at the boundary 
between the palisade and sponge tissues. These are leaf vessels that you have 
cut transversely. You may already be familiar with the types of cells in them 
from other objects we have looked at. They contain vascular bundle tissue with 
tracheary elements and are usually also surrounded by thick-walled cells of the 
reinforcement tissue (see also Chapters 11 and 12).

Needles from firs, pines, or spruces are leaves too. However, since they don’t have 
clearly defined upper and lower sides, their internal structure is a little different 
than that of deciduous plants (in contrast to the evergreen needle trees, decidu-
ous trees lose their leaves each winter). But a nice, thin section of a pine needle is 
an aesthetic pleasure that you shouldn’t miss. The same also applies to the leaves 
of many grasses, which often have very interesting cross-sections.

The inner surface of the lung of 
an adult human is as large as a 
4-bedroom home? In fact, the inner 
surface is 90 m2 on average! That 
makes it clear how effective the fine 
branching of our air passages is. A 
horse that is able to9 run very fast 
can even have an inner lung surface 
of 500 m2.

Because of its many branches, the lung has a very 
large surface area.

Cross-section through a needle leaf (tamarack)

Cross-section through a lilac leaf

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