[For this illustration, Wes wanted to draw a monster that had more to it than what would be visible on the surface. When he drew it, he had no idea that I’d be discussing, among other facts, a guy from a few centuries ago who believed that plants possessed small stomachs at the base of their stems.]
The backyard is a place to make all sorts of interesting discoveries, far beyond the kind you make when you step without looking and you realize that the dog’s been exploring the backyard, too, and leaving a trail as he went along his way.
No, there’s more to the backyard than what naturally might be found there, way more than even invasive plant life or migratory animal species. In my backyard, or more specifically very close to it, are a couple of independent garden centers that offer plants native to parts of the world I have yet to visit. Thanks to them, I can see up close the types of plants that grow as far away from me as Central and South America, plants like the cactus Cereus uruguayanus form ‘monstrosus,’ and I don’t have to pass through the imagination-churning haze created by travel-sickness meds to do it.
Even if the way that some of those plants look make me think that I did.
Cereus uruguayanus form ‘monstrosus,’ which you see in the picture just up and to the left, looks to me like an organism that burst forth either from an alien spacecraft or from somebody’s stomach. It’s bulbous, lumpy, and oddly proportioned. As I learned at the start of puberty, when my nose grew to fit what would be my adult face, objects that are bulbous, lumpy, and oddly proportioned tend to be labeled “strange.”
But this cactus, like all cacti, are less exotic than I had originally thought. So far in human history, researchers have identified and described more than 2000 species of cacti. All of them, except for one, are believed to be native to North and South America (and that one’s ancestor is thought to be a brave little emigrant that survived a trip to Africa as a seed in a bird’s belly). Cacti are, by and large, prickly Western Hemisphere homebodies. No wonder I enjoy their company so much.
Yet while they are native to one side of the world, cacti can reach far and wide—most notably through their roots. There are several strategies for survival that plants in the low-water desert employ. One is to grow a very long central root, called a tap root, so long that it reaches into the water table, the level underground completely soaked with water. Plants like the smoke tree employ this strategy.
Another strategy is the one that cacti use, which is to grow, in addition to a short tap root, far-reaching lateral roots that stretch throughout the shallow parts of sandy desert soil, maybe four to six inches deep. By staying close to the surface, these roots leave themselves ready to absorb any rain that might fall before it can sink farther or evaporate. And they reach far to make themselves available: the lateral roots of a Saguaro cactus can grow as long as its body is tall, and its body can grow as tall as 50 feet.
These long, grabby roots snatch water and carry it to the body of the cactus, where the plant uses it for nourishment. And like the water that a cactus’s roots absorb, our understanding of how plants process their liquid nutrients has come a long way.
As Ruth Kassinger describes in her book A Garden of Marvels, there was a sizable chunk of history during which dissections and examinations with microscopes weren’t exactly everyday activities, mostly because the microscope as we know it had yet to be invented. During this time, thinkers like Girolamo Cardano, a prominent physician of the sixteenth century, used a lot of reasoning by analogy. After all, how different could one living being be from another? The result was that suggestions like that of Cardano, who believed that plants possessed stomachs too small to see just below their stems or their trunks, occupied our brain space for a while.
We can’t fault people for doing the best they can with the resources they have available at the time. Who knows what we’ll uncover about plants in the future? For now, we know that plants are autotrophs, meaning that they make their own food from materials they take in from the environment around them.
We also know that cacti are a kind of plant called a succulent, which can store the water that it will turn into fuel for its cells deep in its tissues until nighttime, when the hot desert sun is less likely to bake it away as the plant goes through its metabolic processes. Some plants, like aloe and agave, are leaf succulents that store their water in their green, fleshy leaves. Others, like Cereus uruguayanus form ‘monstrosus’ and other cacti, are stem succulents that let their stems bulge out like big, mutant brain blobs with all the water they hold.
In fact, that’s why so many cacti have folds and ridges, also known as ribs, along the length of their bodies: as they absorb more water, the ribs unfold and expand like an accordion being opened, allowing the cactus to store as much water as possible. This is where it fails to think in analogies: unlike in humans, water retention in cacti is generally welcomed.
Cactus stems have adapted to life in hot, dry climates in another amazing way. I mentioned that plants are able to make their own food, an ability that has me jealous at times, especially when I’m craving cookies as badly as I am right now. Plants aren’t bakers, but they do make a simple form of sugar through a chemical process called photosynthesis.
Photosynthesis makes sugar from water and carbon dioxide that the plant has absorbed, with energy from sunlight to power the whole reaction. Most plants like trees and flowers perform photosynthesis inside of their leaves. Leaves are wonderful for absorbing sunlight, being as big and flat as they are, but they have one disadvantage: they’re lined with pores through which water vapor can escape. For desert plants, which come across water so rarely, this is a problem.
So cacti found a clever way to avoid this problem. They simply started doing photosynthesis inside of their stems. That’s why cactus stems are just as green as the leaves of your average oak tree—they’re the site of photosynthesis.
You might wonder, in that case, what happened to any leaves that cacti once had. Believe it or not, cacti still have them. Sort of. They’re just modified and quite different from the leaves you’d see on a maple or an elm. They’re thinner, made of a harder material, and often growing in clusters to provide shade to the rest of the plant. Oh, and they hurt like hell if you ever touch them.
That’s right: the spines of a cactus are actually leaves that also have changed to work best in desert life.
It’s one of the reasons why exploration is so great. Even the details that we take for granted as familiar features can become something new with a slight change of perspective. A leaf becomes a spine in a hot desert climate; a plant’s stem becomes a reservoir for water. One time long ago, I slipped while I was in my backyard cleaning up after the dog. Suddenly a few minutes dedicated to scooping poop off the ground became a few minutes spent lying on my back on the grass, gazing at the sky as clouds rolled over a beautiful stretch of blue.
Yeah, definitely a change in perspective.