Last week, I was walking down the street, doing something I pretend I am above: staring into the depths of my phone, and walking. I know better. I swear. And yet, there I was, having a discussion with a friend about someone who didn’t know about the Wu-Tang Clan. And then the universe struck back at my pettiness, in the form of a tree branch, which smacked me right in the face. Conveniently, it also gave me the idea for this post. There I was, a bit stunned, staring at the bare branch’s buds.
Unlike the often cryptic lexicon of natural history nerds, I think everyone knows what a “bud” is. Go ahead and imagine it. I think of a smooth, oblong capsule on a bare branch. Maybe you’re thinking of a sticky green inebriant, which is fine, it’s still a bud. However, let’s consider the buds that are already, or on the verge of bursting: the buds of deciduous trees and shrubs, woody plants that don’t die back to rootstock or reestablish from seeds annually.
What is a bud?
In their most general form, buds house undeveloped leaves and flowers, a place for them to overwinter (and yes, there are many exceptions to this generalization). In late summer and fall, before a plant goes dormant, they put on buds for the following spring. Such buds develop into leaves replaced annually, promote outward growth on stem endings, or burst into flowers. Buds are important, because for the deciduous trees and shrubs of our region (native or otherwise), they are the means of being ready for spring after a season without actively making food.
By late summer, most plants are done growing. Now the focus becomes banking the remaining sunlight in the form of protected bundles of cells. Nutrients in existing leaves will be jettisoned and bare branches are left with only the hint of the life that exists beneath the surface. Buds sit and wait, a little packet ready to be the initial bit of growth every dormant plant needs come spring.
With a little attention you will notice that there are a lot of different types of buds. Most are covered in some sort of modified leaf, scales or hairy coverlets that protect them from harm, whether from animals or the cold. Flower buds tend to be large, and in the case of magnolia buds, are both large and hairy to keep them from freezing. Others can be waxy and sticky (as a deterrent to potential consumers), like the buds of black cottonwoods, Populus trichocarpa. Some contain both flowers and leaves, like Indian Plum, Oemleria cerasiformis, which burst into leaf and flower last week. The bottom line is that when spring comes around, buds need to be formed and ready. Otherwise a dormant plant won’t be able to produce the energy needed to grow new leaves and flowers.
Practically every deciduous plant on the Hill is currently either breaking bud, or getting ready to. Though learning to ID plants by their buds in winter is a supremely satisfying (and nerdy) thing to do, better yet is to simply watch in anticipation of the flowering and leafing out yet to come. Plums have been blooming for a week now. Cherries are not far behind. Certain species of maples are just about ready too. With them come the first flying insects and our first insect and nectar eating birds.
But, how do plants know when to come out of dormancy? We certainly get fooled into wearing short sleeves when the sun shines an ephemeral blaze after days of gray. Plants have been around millions of years longer than we have, so we can safely assume they’re well equipped to handle this challenge. Broadly speaking, plants pay attention to the length of the night, and to a lesser extent, the temperature to figure out their annual timing. This keeps them from making mistakes. Temperatures can fluctuate wildly and trick some plants on the edge of waking from their slumber, but daylight is consistent year, after year, after year and a far better bet.
When plants experience a sustained lack of daylight in fall, they start blocking the channels to buds with a hormone called abscisic acid. With the channels that would normally send food and information cut off, buds sit and wait until they are called upon again. As nights shorten and the days warm (and a certain number of days of cold rack up), something clicks and the hard stop is chipped away at until the bud is back in business. How this works in all plants is still be studying and has deep connection to plant evolution, partially what keeps me coming back for more in this nature study stuff.
There are many ways to describe buds. Terminal buds are at the end of a stem, axial buds face outward from the stem, and adventitious buds show up in abnormal places in response to environmental factors. Buds can be scaly, hairy, or naked of covering. Buds can hold future vegetative (leaves), reproductive (flower), or a mix of both within their layers. However, buds are a nearly universal feature of a growing plant, whether waiting out winter or getting ready to put forth flowers. Buds can tell us a great deal about the life histories of the plants that bare them.
Whether you like to smoke flower buds or enjoy cherry blossoms in March (I recommend a combination), they’re worthy of our attention. These quiet, almost innocent forms have held us in thrall likely as long as human memory has existed: a promise of warmth, beauty, shade, and food to come.
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