It’s that time of year when buds are starting to break their winter dormancy. In December 2014, Daniel and I went for a walk through the Carolinian Forest at UBC Botanical Garden to investigate and photograph buds. We found lots of them! I’ve chosen a few of the photos we’ve taken to highlight some interesting facts about buds.
Today we feature a comparison of two types of mixed buds: the large, scaly brown buds of Aesculus glabra, or Ohio buckeye, and the long, smooth light brown (and looking orange against the blue sky) buds of Fagus grandifolia, or American beech.
A bud can be thought of as a condensed shoot, from which embryonic leaves and flowers arise. At the centre of the bud, on the end of the bud’s short stem, sits a growing point. The growing point is surrounded by an inner layer of leaves, densely folded and crinkled to fit a large surface area into an incredibly small space. In temperate shrubs and trees, the outermost layer of the bud is often composed of thick, tough leaves that form the protective scales (or cataphylls) that we can see in the photographs. These scales come in all sorts of shapes, sizes, colours and textures, from the satiny smooth American beech buds to the rough, sticky scales of Ohio buckeye.
There are many ways to categorize buds. Both buds featured today are scaly, as opposed to naked or hairy. They are also both resting, which means that they formed at the end of the growing season, and will resume growth soon this spring. Another commonality between the Aesculus glabra and Fagus grandifolia buds shown is that they are both mixed buds, meaning they protect both developing leaves and reproductive parts. One final way to describe buds relates to where the bud is formed. Both photos show a terminal bud located at the tip of the stem, and one or more axillary buds located at the axis of a leaf. Sometimes, buds form in other places; these are called adventitious buds, and can be found on roots, at the inter-nodes of the stem, on callus tissue at the cut end of a stem or root, or on the edge of a leaf blade.
Once the growing season resumes, the stems within the buds will begin to elongate and grow. Terminal buds will continue to lengthen the shoot, while axillary buds will form new branches. It is possible to use the scars left behind by terminal buds to age a shrub or tree. Each growing season is represented by a terminal bud scar, which looks like a series of narrow grooves around the twig.
This is also a good time to point out the little, light-coloured bumps found on the stems of both the American beech and Ohio buckeye. These bumps are termed lenticels, and are small openings in the stem’s bark that allow oxygen and carbon dioxide to pass in and out of the stem. Like scales, lenticels can also take on different forms; the horizontal “stripes” found on cherry trees is an example of lenticels that looks quite different from those shown today.