Friday, March 1, 2013

Hey Buds!

Today felt like winter, but if you read nature instead of reading the thermometer, spring is already here.  Tree buds are among the first things to reveal that winter is over, and many of the buds at our outdoor classroom are already saying spring.  Twigs are the ends of tree or shrub branches, and the caps at the end of twigs are called buds.  Buds are the most exciting things about twigs (and trust me, there are a lot of exciting things about twigs).
Buckeye twig with three buds.  The end bud is starting to open.
Generally, ends of plant parts are very important, because these parts contain the only plant structures that can make new growth.  Parts capable of plant growth are called meristems.  Look at the end of a tree’s twig and you will see a structure called a bud.  Each bud contains a meristem covered with tiny leaf-like things called bud scales.  Scales are the protectors that keep the meristem inside from dying in the freezing cold of winter.  This time of year, the meristem starts to grow, and it pushes the scales aside.  As the meristem grows, it starts to produce either new leaves, stems and twigs or new flowers.   If you’re curious, cut off a swollen bud, slice it in half from top to bottom, and look at the cut surface with a magnifying glass.  You’ll see sliced immature leaves or flower petals.
Large buckeye bud just starting to open.  Notice the bud pushing the bud scales aside.
Plants grow very differently than people do.  People get longer and wider in every area of their bodies as they grow from child to adult.  So your arm in first grade will be both shorter and thinner in all sections, upper and lower arm, hand and fingers, than your arm in the twelfth grade.  Most plants only grow longer at their tips. (Can you guess what plants don’t grow from their tips?)*  Imagine if your body only grew longer at the ends of your toes and fingers – your adult body would look VERY different.  Plants’ stems (including tree trunks) and roots can grow wider at any point, which is why it takes more people to hug around old trees than young trees, but they only grow longer at the tips.  People often think that if they were to carve something into a tree and come back in 20 years, the carving would be very high off the ground.  This is false, since trees only get taller at the ends of their branches.  [Just a reminder, please don’t carve things into trees – tree bark is the plant organ that carries food between the roots and the leaves, and damaging the bark can kill a tree.]

Back to the buds.  Look at several trees and shrubs at the outdoor classroom.  Right now many trees have some buds just starting to open and other buds in their closed-up winter stage.  It’s a great time to compare winter buds and spring buds on the same plant.  Notice the different shapes of bud scales – pointy or rounded, separate or overlapping, striped or not, green or brown.  You might also notice how some twigs become very colorful just as their buds begin to expand.
Rhododendron flower bud
My favorite thing about buds is that bud scales leave scars on the twigs when they fall off.  Bud scale scars look like tiny clustered rings around a twig.  If you look at a twig starting at the tip and move back along the twig, you will encounter several tiny rings in the same place running around the twig like tight bracelets.  Those rings are scars from where last year’s bud scales were, and everything from there to the tip is last year’s new growth!  Look further down the twig toward the main branch and you may find additional years’ of bud scale scars.  You can tell the age of a twig by counting back bands of bud scale scars from the tips to the trunk.
Rhododendron flower bud opening.
*Grass and other grass-like plants grow from meristems that are near the ground.  That’s why we can mow the grass and cut off all the leaf tips but the grass keeps growing and needs to be cut again soon.

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