On Seed Dispersal, or, One Day I’ll Fly Away—Or Be Launched, Whichever

I use witch hazel extract on my face every night. It’s derived from the leaves and bark of the common witch hazel plant, Hamamelis virginiana, and in addition to cleaning the skin is supposed to help relieve it of irritation. In light of witch hazel’s calming properties, I guess it’s a little funny that a witch hazel plant starts out, very literally, with a bang.

For a plant to produce offspring and continue that beautiful circle of life that Elton John sang about, it has to send seeds out like children into the big, bad world, a process known as seed dispersal. And just as some parents and caretakers allow their children to keep living at home after graduation, maybe staying in the basement or the pool house, while others practically pack their kids’ boxes and suitcases for them, plants go about seed dispersal in any number of ways:

The photo that inspired this post.

• Letting gravity take its course

• Encasing their seeds in tasty fruits for animals to eat so that the seeds will later be, um, deposited (seed dispersal plus, now with a fertilizer bonus)

• Attaching lightweight structures that allow the seeds to drift serenely on the breeze

• Launching them violently into the surrounding environment

That last option probably sounds made-up. It isn’t. Witch hazel seeds develop inside of a capsule that bursts at maturity. Like a circus daredevil spewed from a cannon, each seed ends up shot about twenty to thirty feet away from the parent plant. The capsule makes a popping sound upon bursting—or a bang, to go back to where we started this.

It’s nothing like the method of seed dispersal that many trees here in the Midwest employ. Wind dispersal seems more appropriate for a plant that’s used to make a soothing extract. The way that whirlybirds or helicopter seeds like the ones seen in the photo above (the technical term for a winged seed like these is a samara, presumably because “whirlybird” never stuck in scientific circles) simply flutter to the ground perhaps offers a greater sense of enchantment than the botanical equivalent of cannon fire. Plus, as mentioned before, all the other plants are doing it: various trees including ashes, the winged elm (naturally), and most conspicuously maples all produce winged seeds.

So why doesn’t the witch hazel plant give in to peer pressure? Well, as helpful as winged seeds are in spreading a plant’s offspring far and wide, that huge range of dispersal (we’re talking hundreds of feet here) comes with certain trade-offs:

1. Not every seed is guaranteed to land somewhere hospitable and grow, so the parent plant spends a lot of energy producing seeds that will never germinate.

2. In order to be light enough to dance on the spring breeze, winged seeds aren’t packed with as much nourishment as, say, the seeds packed into fruits are. As a result, some will be too poorly nourished by the time they land to sprout.

3. Kids like to pick them up and toss them into the air, at least where I grew up, because it looks really neat (see trade-off #1).

No doubt that witch hazel’s exploding seed pod looks (and sounds) neat, too, but the exchange there is that it takes even more energy than making a load of winged seeds to actively expel a few seeds from one’s body. Each plant evolves the method of seed dispersal best suited to its environment. If it happens to delight us with showers of whirlygigs or sudden eruptions of seed pods, well, that’s just one more way we’ve benefited from evolution, I’d say. It’s right up there with opposable thumbs in scientists’ minds, I’m sure.

Monsters Mini-Post: On Uncontrolled Growth and the Gall Some Bacteria Have

It’s bacteria’s world; we’re just living in it.

At least, that’s how it appears. Bacteria inhabit just about every untreated, unsterilized surface and environment on the planet. And our bodies happen to provide some of the best habitats for colonization.

Propionibacterium acnes is a bacterium that lives on human skin, deep in the pores, specifically. It hangs out near the sebaceous glands, which are the tiny glands near each that produce the oil, or sebum, each of us has lightly coating our skin and hair. P. acnes‘ strategy for life is pretty similar to the one I employ at county fairs and carnivals, which is, simply, to eat as much grease as possible. By taking up residency near the sebaceous glands, this itty bitty bacterium gets a nearly endless supply of the sebum it prefers to eat.

Unfortunately for the human host, whenever too much sebum and too many bacteria clog a pore (and whenever the body starts reacting to what it perceives as a big bacterial infection), acne can develop. A bunch of tiny bacteria can be all it takes to produce a huge, honking zit.

Our bacterial bumps aren’t nearly as bad as some of the ones plants develop, however.

Agrobacterium tumefaciens is another bacterial species with a long, lovely name. It infects plants, not humans, though the list of plants it can infect is substantial: roses, willows, maples, raspberry bushes, apple trees, cherry trees, almond trees—you get the idea. It’s a wide-reaching bacterial agent, and it’s pretty sneaky to boot.

A. tumefaciens enters a plant’s system through a fresh wound, one created through pruning and other forms of mechanical damage. Once inside, it does more than divide and conquer: it makes the plant’s own cells divide and conquer. Like a mad scientist minus the hysterical laughter, A. tumefaciens actually splices its own DNA into the DNA of a plant cell. The new DNA sequence tells the plant to produce growth-stimulating hormones. Under the hormones’ influence, the plant cells multiply so much that a cyst-like lump called a gall develops. Lo, A. tumefaciens gets a spacious new home inside the plant tissues!

Meanwhile, circulation of water and essential nutrients within the plant gets cut off.

Although galls can develop along the stem or on the roots, A. tumefaciens is mentioned in conjunction with what’s called crown gall, which is a lump that develops at the plant’s base, right around the soil line (the area known as the crown). The recommended treatment for crown gall? In the case of young trees, it’s sometimes believed to be more economical and better for general plant health to remove the plant. Older, larger trees can have the gall removed surgically or left with the plant for the rest of its woody days if the plant is otherwise healthy.

So if ever you or someone you know ends up lamenting a sudden, uncontrolled outbreak of acne growth, just remember, it could always be worse. At least your DNA is still your own, you know?

Crown gall photo credit: ForestryImages.org. Image made available on Wikimedia Commons through a Creative Commons Attribution-Share Alike 3.0 United States license.

On Naked Buds That Are Actually Hairy Buds, or, Hey, Buddy

Military strategy and botany aren’t often considered in the same essay, but hey, sometimes it’s necessary to talk about defense.

The Greek phalanx is perhaps one of the best-known formations in military history, and not just because Gerard Butler drew attention to it with his astounding abs. The phalanx was a pain in the ass to penetrate: while Greek infantrymen—foot soldiers known as hoplites—stood in a tight cluster with their meter-long shields overlapping, they also stuck long spears through the gaps, daring anyone to come close and try to penetrate the dome of bronze and leather created by the shields. It wasn’t the easiest formation to maneuver through a battlefield, but it largely kept the hoplites safe.

The photo that inspired today’s post.

Plants, in contrast, generally don’t have to worry about moving anywhere, unless we’re talking about seed dispersal or Ents. They do, however, have to deal with insects and other herbivores gnawing on them, especially on their tender green buds (which sounds a little more pornographic than it really is, sorry).

Woody plants have two types of buds along their branches: leaf buds, which produce the small, leafy shoots that we also know as twigs, and flower buds, which pretty much let you know via their name what they produce. In either case, the bud is a site of fresh new growth for the plant, which means that the bud is important to protect.

Plants aren’t animals, though (and if this blog teaches you nothing else, let that be it). There is no ability for a plant to go all Mama Bear on invading insects and simply swipe them away, as impressive as that would be. Most woody plants instead protect their buds with bud scales, modified leaves that hide the new green growth. Like the shields, or hoplons, of the Greek foot soldiers, the scales often overlap. They also have a leathery texture; the hoplons, made partly from wood, had leather fastenings that allowed soldiers to secure the shields against the entire length of their arms.Granted, buds lack the bronze embellishments of hoplons, but you know, details.

But not every plant’s buds are covered by scales. Some plants, like sumac and the peach tree, as well as other herbaceous plants (which are plants with leaves and stems that die back to the ground every year), have buds covered with tiny hairs. Because they lack scales, these buds are considered naked buds, which means that, yes, like your last date, plant buds can be both naked and hairy. Hey, buddy, indeed.

The hairs serve a similar purpose as the spears of the phalanx did: they keep attackers away. Specifically, they do an excellent job of preventing critters like caterpillars from munching on the bud tissue, which the hoplites never had to contend with, but the principle is close enough. In this way, the world’s flora demonstrates how adept it evolved to be at fending off onslaughts.

Nature: it’s a battleground. And war can get hairy.

On Wood Decay Fungi, or, That Dying Tree Is More Alive Than You Think

[When drawing this monster, Wes said that he wanted to give it flat teeth specifically because the flat edges of incisors are specialized for chewing vegetables and plant matter. Essentially, he made the tree something of a cannibal. I think it works pretty well with the following discussion of non-animals consuming each other.]

The photo that inspired this post.

You know, of all the items in the world that can make people so giddy that they get stupid, pruning shears probably shouldn’t be on the list.

And yet I’ve seen homeowners as well as public works employees let the power that a pair of steel shears imparts lead them to some questionable choices while they pruned dead, spindly branches from trees. They approach pruning as if they were swordfighters in a martial arts epic, or people who decide to re-evaluate their phones’ contact lists after a Saturday night out drinking. Either way, they cut with a vigor that borders on hysterical joy, leaving very little when the act is done.

Pruning, however, is a delicate art. As with swordfighting and social interaction, there’s a way to do it that’s right, and several ways to do it that just leave a mess. A bad pruning cut can create a gaping hole of a wound in a tree’s wood that a certain group of parasitic organisms would love to crawl inside and infect.

First, though, before we take a trip into the nightmarish-sounding world of one living organism easing its way into another (ohmigosh, I’ve seen Alien, I know how this is going to end), let’s take a quick look at tree anatomy:

At the base of a tree branch, right where it connects to the tree trunk, is an almost turtleneck-type collar of tissue called the branch bark ridge. This ridge is the part of the tree where new wood will grow after a branch is cut away. The wood that grows back is called either wound wood, which sounds vaguely S&M-ish but isn’t, or callus tissue, which sounds like something the tree should have taken care of on a spa day.

Unlike the patches of dead skin that we loofah away from our heels, calluses at the site of a removed branch are good. They prevent disease organisms from infesting the wood deep within a tree. Too often, though, the branch bark ridge is pruned away along with the rest of the branch. The pruning cut is made flush against the tree trunk, and it’s not just a flesh wound, or, in this case, I guess, a flush wound. Without the branch bark ridge, callus tissue can’t form.

And that’s where the fungus comes in. Like, literally where it gets into the tree.

Fungi are fascinately deceptive organisms. It’s easy to believe that a mushroom is the main part of a multicellular fungus, because that’s the part that we see. More importantly, it’s the part that we eat (assuming the shroom isn’t toxic), and sometimes, we just need to know enough to know what’s going to taste good on a pizza without killing us. It’s all about priorities.

A mushroom is only a reproductive structure, though, a part that pops up when the fungus is ready to release its spores into the wind and go forth and multiply across the land, even if “the land” is just the several-yard radius of the front lawn. What a fungus really is is a collection of filaments called hyphae. Each hypha is a group of cells that looks like a thread and that grows snaking its way through dark spaces, often joining with other hyphae in a big clump to form a mass that’s called a mycelium. Patches of dirt and soil make excellent places for fungal hyphae to develop into more massive organisms.

So do the insides of trees.

If an external wound in a tree isn’t sealed with callus tissue, it leaves the tree’s sensitive inner tissues, the channels that carry water and nutrients from the root to the stem, exposed to creatures that want to devour them. Once fungi make their way into an open wound, it isn’t hard for them to reach their hyphae all the way through the tree’s otherwise hidden nooks and crannies. It’s everything that makes you squeamish when you read in some kind of sci-fi story about a tentacle monster trying to stick its tendrils into any crevasse it can find on the hero’s body, except that it happens on a much smaller scale inside of wood, and it happens every day around the world. Oh, and, in a way, it’s even more violent.

Fungi are heterotrophs, meaning that they have to consume external matter to get the nutrients they need to live. Humans are, too, so we have something in common. However, human beings politely digest their foods inside their stomachs, away from the view of one another. Fungi? Not so much. They engage in what’s called extracellular digestion: they secrete enzymes from their bodies, decompose the substance of a tree outside of themselves, and then absorb the broken-down nutrients through their cells. Imagine if you ate your grilled cheese by slapping your hand down onto it, secreting some acidic chemicals from your hand that decomposed the sandwich into mush, and then absorbing good nutrients from the mush through your skin.

I can’t lie. Part of me finds that a little disturbing; the other part of me is impressed. Would you believe, though, that some plants actually need fungi to do this in order to survive?

The fungi that consume a tree through its innermost heartwood are considered parasitic, meaning that they benefit while the trees that host them suffer. Fungi that eat dead matter are called saprophytic. Many fungi, though, benefit the plants they’re living on as well as themselves when they invade. These fungi are called mutualists, and they most often make their way through a plant’s roots.

Orchids in the wild serve as a widely known example of mutualism. When fungal hyphae invade a plant’s roots, they create a hybrid structure called mycorrhizae. As botanist Hans Burgeff discovered in the early 1900s, when certain fungi attach themselves to orchid roots, they carry nutrients from deep within soil up to the orchid and share them via the channels created when the fungi invaded. The orchids get an extra source of sustenance that their roots didn’t reach; the fungi get a host that provides them with sugars made during photosynthesis. When mycorrhizae are involved, everyone wins!

Hardwood trees like elm and ash trees can benefit from mutualistic fungi, too. A biologist named Stewart Miller has shown that these trees are excellent hosts for the morel mushroom, a tasty fungus that, like many culinary delicacies, can be described as “freakin’ weird-looking.” The tree gets deep-soil nutrients; the fungus gets to suck on some tree sap. Of course, the fungus doesn’t actually produce those delicious mushrooms until the tree starts dying a little, sending the fungus into a Jor-El-like “last-ditch attempt at survival” mode, so there’s that downside.

As destructive as the activities of lignicolous, or wood-dwelling, fungi may seem it’s important to remember that fungi play crucial in outdoor habitats. They break down the dead tree stumps that otherwise would pile up on the forest floor, and they make the nutrients from dead matter available for plants to use so that they can grow. Even when fungi hollow out a tree trunk, they create holes that creatures like squirrels and owls use as homes. (Fun fact: standing dead trees that animals occupy are known as snags.)

Basically, thanks to fungi, a dying tree still gets to participate in life, and without all the hassle of returning as a zombie-tree or as some kind of cannibalistic tree-monster as seen in the drawing above. That seems like a pretty good arrangement to me.

For a list of some common wood rot fungi, click on this link. Have your own experiences with tree snags or with lovely lignicolous fungi? Leave a reply and let us know! (Be sure you’ve clicked on the individual post link to see the reply box below!)