How Buds on Trees Survive the Cold (and Related Mysteries)
Return to Biology Index
Ben Stark Illinois Institute of Technology
Chicago IL 60616
This science "mystery" was originally presented to second and third graders,
but is probably appropriate for grades 2-6. The objectives are (1) to see how
the delicate tissues of a tree bud are insulated so that they can survive the
winter, (2) to learn how to determine the age of a branch/twig, and (3) to see
how growth of branches can vary from year to year.
Several small branches/twigs, taken from, preferably, a horse chestnut (buckeye)
tree in late Fall or Winter (after the leaves have all fallen).
razor blades (for younger children, to be used by teacher only)
This lesson makes a perfect "science mystery." One way to introduce it is to
ask the children how they stay warm in the Winter (they stay inside and their
houses are heated, they wear warm clothes, they sleep under blankets, etc.).
Then you show a branch and focus on the "terminal buds" on that branch (the
terminal buds are those at the end of each branch). You point out that the
terminal bud contains a baby stem and baby leaves and remind them that these
"babies" have to stay warm all Winter also. The mystery is, how can they stay
warm without the advantages the children have? You might remind the children
also how cold it has gotten outside that winter.
Then show the children the outside of the bud(s). Note that the buds are
covered by a series of hard overlapping "bud scales." Then, using a razor
blade, slice open one or more buds laterally (left to right) through their
centers. Observe with the aid of the hand lenses (or with the naked eye if no
lenses are available) and perhaps make a drawing of what is seen.
Things to notice in particular are the many layers of the bud scales on the
outside of the bud, the "baby" (embryonic) shoot and leaves in the center of the
bud (which might be a bit hard to see), and the "cottony" packing material which
tightly surrounds the shoot/leaves underneath the layers of the bud scales. The
answer to the mystery, then, is that the embryonic shoot and leaves are
protected from the cold by both the layers of bud scales and the cottony
material, and so are able to survive the Winter cold.
In the Spring, the embryonic shoot/leaves in each bud begin to grow. As they
do, they shed the cottony material and the bud scales, which fall off the
branch. Loss of the latter produces a series of bud scale scars at the base of
the former bud; these look like a series of (mostly) parallel lines around the
circumference of the branch. The position of each group of bud scale scars,
then, permanently records the position of a terminal bud that had existed at one
time in that position on that branch. The distance between adjacent bud scale
scars on a branch represents the growth of that branch in one growing season
(this might open a lively discussion by determining if the growth of a branch
had been the same in each year and, if not, what variables--heat, rainfall,
etc.--might have led to growth variations). The overall age of the branch can be
determined by counting the number of groups of bud scale scars on it. Note that
if your branch has smaller branches growing out of it, they will have to be
younger than the main branch, and this should be confirmed by the bud scale
patterns on each.
Students could be graded on their diagrams of the dissected buds, with points
given for accuracy, neatness, detail, and correct labelling. You could also ask
students for a short written report covering such topics as the age of their
branches (and how they determined them), if there was variable growth from year
to year in the branch and how this was determined, etc.
Probably any good high school or college general biology or botany text would
be a useful resource for this activity.