Botany for Gardeners: Cells are Miracles that live Everywhere

I just finished reading my introduction to Botany, written by Brian Capon which I hope has prepared me to work through this behemoth of a textbook in the long, cold dark ahead. It's a fairly well-written book, and concisely describes the basic parts of a plant's anatomy their functions. After reading Michael Pollan's visceral, no-bullshit take on plants, which really gets you feeling and thinking like a plant might, this botany book tastes a bit sterile. The author also vacillates between glossing over subjects because the reader is not knowledgable enough and neglecting to mention important basics. Neither of these problems really detract from my overall opinion, however.

If there's one message I took away from this book, it's that plants are inconceivably complex, sublimely beautiful, and capable of feats of chemical engineering that humans will never match. They make and store their own food from sunlight, air, and water. Think about that for a second: with those ingredients, the average human would end up with sweat, urine, and a sunburn. Plants use that food along with minerals in the soil to reach deep underground, fan out over the earth, and reproduce. Reproduction isn't as easy as it is for us, either. Most plants either fill the air with enough pollen to choke a horse and hope it lands in the right place, or they produce delicate, colorful, fragrant structures that trick totally unrelated species into hand delivering the pollen where it needs to go. All with chemicals of their own making.

Sorry to bother you, ma'am. I'm here to clean out your
stamens and give your stigmas a once over.

If you have even the slightest interest in plants, you should read this book. It's a pretty easy read, and you'll start to appreciate grass, trees, and even your food in a whole new light. Before you go, though, I want to share two of the most striking subjects the book taught me about: seeds and stems.

Stems support the weight of the plant and its leaves, but might only be a few hundred cells across. The cells vary in type and size throughout the stem, each acting in concert with those around it to execute the functions of the plant. Let's look at the Lamium orvala (AKA Deadnettle) at right. The thin, light green stalk from which the leaves and flowers are growing, is the stem (I know, this is tough stuff to grasp). That stem has a relatively tough layer of cells around the outside to keep water and nutrients in and pathogens out. Within that there are bundles of cells that transport water up from the roots to the leaves and flowers, some that transport food down to the roots, and others that primarily divide to make the stem thicker as the plant grows up. Here's a beautifully prepared cross section of a deadnettle stem:

Before you go out and buy a microscope, understand that this stem was professionally sliced and dyed to look like that so it's easier to identify different structures. Every one of those globs is a plant cell, but they're all fulfilling lots of functions. Here are some of the tissues of a plant stem, as seen in deadnettle:

1. This row of small, tightly-packed cells is the epidermis, or skin, around the stalk. It prevents water loss to evaporation, and keeps out invaders like bateria and fungi that would infect the plant and destroy it.
2. The red cells here are xylem cells, which carry water absorbed by the roots up into the leaves and flowers of the plant. They are long, tubular cells that retain their sidewalls, but lose the top and bottom caps, allowing water to flow more quickly than it would through the cell walls. These vein-like structures are what spittlebugs, aphids, and other true bugs tap into when they feed on a plant.
3. The larger blue cells outside the xylem bundles are called phloem, and they carry the nutrients made by photosynthesis from the leaves to the roots, where they can be stored for use later. You can see the phloem forming a ring about 2 cells wide all the way around the stem. (remember PHloem = PHood)
4. This brown-looking group of cells, called the cambium, continues all the way around the cell between the large teal cells (see E) and the blue phloem cells. Its cells divide frequently and occupy space in one of three directions. Cells that end up inward become xylem or parenchymal (see E) cells, those that go outward become phloem cells, and some move sideways to make sure the cambium remains intact as it and the stem increase in circumference. In this way, the stem only grows in girth from within. A separate organ, an apical meristem* grows from the top of the plant, laying down new layers of cells to lengthen the stalk. The cambium inside the stalk can also be called a lateral meristem, since it grows sideways.
5. These big, blue beauties are called parenchymal cells, and they make up the bulk of plant tissues. They can store waste products, secrete healing resins, store fats and starches in roots, and perform lots of other functions depending on their location. A parenchyma you may have seen today is the pith in an orange.
6. This large space is just that. This stalk is hollow, probably allowing it to sway more in the wind than other plants. Many other green plants' stalks have a cortex made of parenchymal cells.
7. BONUS: I just learned about this kind of cell myself while reading about this microscope slide. The structures in the corners are made of collenchyma cells, which are a bit like xylem cells, in that they are long and tubular. They also grow thickened walls, creating fibrous masses running the length of the stalk. This gives the stalk a lot of structure and helps it stand up straight when it gets moved by wind or an animal. Plants kept in a completely windless place do not grow collenchymae as much as plants that get blown around. The fibers in a celery stalk are collenchymal structures.

And that's all in one species of one type of plant! Woody plants have all these structures too, but many of the cells "die" by building too many cell walls. They don't function as cells after that, but they provide much more structural support that living cells. There are also different types of cambia, xylem, phloem, and parenchymae, and some plants have other structures because of the way they grow. To learn about all of them, you'll have to read the book.

If you think all that's impressive, wait til you hear about seeds. They're indestructible escape pods that allow plants's genes to survive weather extremes and emerge when everything is safe for a new generation to grow. Seeds will be in an upcoming post, once I finish with some...experiments.

Mwahhahahahahahahahahahaaaaaaaaaaaaaaaaaaaaaaaa,
The Regular Farmer

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*"apical" means 'at the apex or end', "meristem" comes from Greek meristos, meaning 'divisible', and German xylem, meaning 'wood.'

-Photo Bee and Flower: Author: John Sullivan Source: pdphoto.org. Public Domain.
-Photo Lamium Plant: Author: Kurt Stüber. Creative Commons Attribution-Share Alike 3.0 Unported License
-Photo Lamium Cells: Author: Micropix. Creative Commons Attribution-Share Alike 3.0 Unported License. I added the letters and arrows.