By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
At the most basic level, the universe is orderly, although sometimes that order is not immediately apparent. Albert Einstein famously remarked, “God does not play dice with the universe.” Fortunately, in the forests of Tryon Creek State Natural Area (TCSNA) we have many wonderful examples of the orderliness of the universe. For this article I will focus on the symmetry that we see in so many of the organisms in the forest.
The most common types of symmetry we can see at TCSNA are typically referred to as spherical, radial and bilateral symmetry. Another way to think about these kinds of symmetry is symmetry around a point, symmetry around a line and symmetry around a plane.
Spherical Symmetry (Symmetry around a point)
With spherical symmetry, there is one point in the middle of an object, and no matter which direction you go from that point, everything is the same. If you’ve already guessed that all the examples are spheres, you’re right! The seeds and fruits of some plants are the best examples of this at TCSNA. For example, the picture below shows the fruit of a bedstraw (a.k.a. “cleaver”) plant (Gallium spp.) The scar in the middle of the picture is where the fruit was attached to the stem.
Other forms of symmetry get a little more interesting.
Radial Symmetry (Symmetry around a line)
A second type of symmetry is radial, where there is a central axis to the object, and the parts all stick out equally in any direction from that central axis. One of the best examples can be seen in this mushroom fruiting body. Imagine the red dashed line going down the center of the stem of the mushroom. At a given distance from the ground, if you travel out at any 90° angle to that red line the mushroom structure is identical.
The picture below is of the underside of the mushroom’s cap. I’ve put in a red dot to indicate the central axis of the fruiting body. No matter which direction you look out from the center, the structure looks essentially the same. The edges of the gills that you see as lines, all point to the center of the mushroom.
Looking at the underside of the mushroom’s cap provides an additional perspective on radial symmetry.
The mushroom above is an example of the simplest kind of radial symmetry. But radial symmetry can be more complicated, and more interesting.
Spirals – A special case of radial symmetry
The mushroom pictured above is a very simple example of radial symmetry, but more complex examples can be easily found at TCSNA. The most obvious are some of our native conifers. For example, at first glance the scales on a Douglas-fir (Pseudotsuga menziesii) cone might appear to be arranged in a random pattern.
In fact, the scales on a Douglas-fir cone are arranged in a definite spiral pattern around a central stalk. The scales are actually arranged in multiple spiral patterns. To illustrate this I painted the bracts (the three-pointed papery structure attached to each cone scale) to highlight these spirals. Each spiral is a different color. The results can be seen in the movie below. Since each cone scale is actually part of three different spiral patterns, I have painted three different cones, each illustrating one of the three patterns. A different color of paint was used to mark each of the spirals. Watch first one cone and then the others to see these three different spiral patterns.
You can see in the movie that there are a set of three spirals of cone scales going in one direction around the cone axis at a very gradual angle. There is a second set of five spirals going around the cone at a steeper angle in the opposite direction. Finally, there is a third set of eight very steep spirals going about the cone in the same direction as the first set of spirals. So each scale is part of all three spirals going around the cone’s central axis.
In any given plant, the number of spirals are a part of a set of numbers known as the Fibonacci sequence of numbers. The Fibonacci numbers were described by an Italian mathematician more than 800 years ago (and Indian mathematicians had apparently described them even before that). Starting with the number 1, each subsequent number is the sum of the two previous numbers. Below is the start of the original Fibonacci sequence (the “modern” version starts with zero, which has no impact on the rest of the sequence):
1, 1, 2, 3, 5, 8, 13, 21, 34, etc, etc, ad infinitum.
In the botanical literature, it is traditionally reported that the number of spirals in any plant are always two consecutive numbers of the Fibonacci sequence. With one exception. The pineapple fruit is almost always described as having three spirals. I present here the possibility that the Douglas-fir cone, like the pineapple, is composed of three spirals, not the traditionally recognized two. But, whether it’s two spirals or three, it represents an example of order in nature.
Bilateral Symmetry (Symmetry around a plane)
Finally, there is bilateral symmetry, which is symmetry with respect to a plane (think of a sheet of glass). The structure is identical on both sides of the plane. The butterfly below is a beautiful example of bilateral symmetry. Think of an imaginary sheet of glass running vertically through the butterfly’s body. Each side of the body is an identical mirror image of the other side. The easiest feature to see in the photo below are the patterns on the wings.
Plants often exhibit bilateral symmetry, as exemplified by the bigleaf maple (Acer macrophyllum) fruit shown below. In fact there are two different planes of symmetry. The first one is centered around the red line drawn on the picture. The second plane of symmetry is represented by the paper on which this picture could be printed. The front and back sides of the seed are identical.
But wait… Not everything in the forest is symmetrical!
My favorite example of a non-symmetric organism in the forest is the banana slug (Ariolimax columbianus). Below are two pictures of the same slug. One picture is of the right side of the forward part of its body, and the other is of the left side of the forward part of its body. As you can see, the slug only has one breathing hole, and it is on the right side of its body. Thus, the slug does not display symmetry in this regard, it is asymmetrical. Every slug has its breathing hole on the right hand side of the body.
But that’s not the only way a slug is asymmetrical! Look at the coloration on the body of the slug pictured below. A black spot on one side of the slug is not matched with an equal sized, or shaped black spot on the other side of its body.
Symmetry is often useful, such as birds having one wing on each side of its body. Imagine a bird trying to fly with both wings on the same side of its body. But In truth, while nature has intended many things to be symmetrical, oftentimes the symmetry is not perfect. These imperfections may result from mutations during development, or accidents. So what you ask? Scientists have discovered that some animals, like female peahens and barn swallows, prefer males with symmetrical tails. To the birds, symmetry could be proof of a potential mate’s normalcy, which is often the safe choice.
The symmetrical patterns that we see in much of the flora and fauna of TCSNA provide some reassurance in the orderliness of the universe. It suggests that perhaps Einstein was correct!
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Mother Nature is the world’s first, largest and best recycler! Each year in Tryon Creek State Natural Area (TCSNA), tons of organic matter like trees, dead animals and coyote feces are recycled. This recycled material is used by the forest to grow new trees, birds and mice, to name just a few. If it weren’t for recycling, the surface of the earth would be covered with unimaginable amounts of dead organic matter. In addition, it would be tough for any new organisms to grow because so many materials vital to life would be locked up in the litter.
Two years ago, I started a small study at TCSNA to determine just how fast the recycling process is in our forest. The first year’s results were published in a Naturalist Note last fall. To access this previous note, use this link, and then scroll to the bottom. This second Naturalist Note takes a look at the results after two years.
How it works…
As indicated in the previous Naturalist Note, samples of five different kinds of fresh organic matter were collected from the ground in TCSNA in the fall of 2014. Collecting them from the ground insured that they were naturally ready to start being recycled. The samples included a) red alder (Alnus rubra) leaves, b) bigleaf maple (Acer macrophyllum) leaves, c) western redcedar (Thuja plicata) branchlets, d) Douglas-fir (Pseudotsuga menziesii) branchlets, and e) scales from a Douglas-fir cone that had been chewed apart by a squirrel. Two samples of each thing were collected, for a total of 10 samples.
Each sample was placed inside a flat “bag” made of standard plastic window screen material. The bags were then taken into the forest, placed down flat on the forest floor, and fastened down by inserting a nail through the corner of each screen down into the ground.
From September 2015 through September 2016, pictures were taken on a quarterly basis. The results after two full years can be seen in the photos below. The first photo shows the array of litter bags before I disturbed them to take the photos. The silvery-gray bits seen in the photo are the exposed part of the screen bags. As you can see, there were also some plants growing up through the litter bag array.
They’ve really changed!
The rate of decay of materials from the different species varies dramatically. Specific samples are shown below. The first two sets of pictures show the two different red alder leaf bags. I’ve included both sets of red alder bags to show that there is a certain amount of bag-to-bag variation in the rate of decay. For the remainder of the species in the study, I’ve included only one of the two bags. You may observe that due to my picking up these bags periodically for photos, the position of some of the materials in the bags has shifted a bit.
While most of the leaf blades are substantially degraded, some of the veins are still intact. This is typical of many different leaf decay studies.
The following photos are of one of the bags containing bigleaf maple leaves. Again, you can see that the leaf blades themselves are pretty well decayed, but some of the veins, and petiole (the “stem” that connects the leaf blade to the branch) are still identifiable.
…Or maybe not so much!
The remaining samples are all from conifers, which retain their foliage for more than a single season. If you could feel their foliage, you could tell it was definitely tougher. This becomes evident in the photos below.
The western redcedar foliage has not only not decayed very much, but also, many of the leaf scales are still attached to the branchlets. I’m impressed!
Most of the Douglas-fir needles in the bag shown below have fallen off the twigs, but they still appear to be largely intact. Detailed scientific studies suggest that while there has probably been some substantial decay inside the needles, the outer tough surface of the needle has been somewhat resistant. One unfortunate thing with the Douglas-fir branches is that once the needles have fallen off the twig, they can easily slip through the mesh screen when they are jostled very much. I have no doubt that some of the needles that were originally on the twig have fallen out of the bag.
The final set of photos below show the tough cone scales of the Douglas-fir which appear to be only minimally changed over the course of two years on the ground. This is not surprising, given that the cones are made tough to protect the seeds of the tree. Also, the cones tend to have high resin content, and thus resist decay.
Litter as fertilizer
Litter contains vital nutrients that help trees grow. One of the advantages of relatively slow litter decay is that the litter then acts as a “slow-release fertilizer” a method of ensuring that the living plants will have ample opportunity to absorb it to assist with their growth.
But long before the nutrients trapped in the litter help the next generation of trees and shrubs grow, those nutrients help the fungus and bacteria that decay leaves grow. And just like you, the microorganisms are more attracted to a lavish banquet than to a bowl of thin soup. The more nutritious the litter, the faster it decays1. For example, red alder leaves have 4 times the nitrogen content of either western redcedar or Douglas-fir foliage. Bigleaf maple litter has more than 3 times as much phosphorus as either western redcedar or Douglas-fir. Both red alder and bigleaf maple have more than 10 times the amount of potassium as Douglas-fir litter. Viewed from the perspective of nutrient contents, it’s no surprise that the red alder and bigleaf maple foliage decays faster.
It was found in the mid-1970s that applying urea fertilizer containing 200 lbs of nitrogen per acre to Oregon’s Douglas-fir forests, significantly increased their growth rate. As noted above, red alder leaves, due to the nitrogen-fixing nodules on the alder roots, contain relatively high levels of nitrogen. The photo below shows the amounts of urea fertilizer (the typical nitrogen fertilizer for forests) and alder leaves that would be needed to provide 200 lbs/acre of nitrogen. So the decaying leaves, especially the alder leaves, are acting as a slow release fertilizer.
The box of dried alder leaves contains as much nitrogen as the small vial of white urea.
The dead plant parts like tree trunks, branches, leaves and even the unseen roots, are important parts of the whole cycle of life at TCSNA, as well as in other forests. In their role as nutrient recyclers, the fungus and bacteria that decay the forest litter play a vital role in helping maintain a healthy and vigorous forest. Recycling is an important example of how different parts of the forest work together to create the TCSNA we love so much.
1Valachovic, Y. S., B. A. Caldwell, K. Cromack Jr., and R. P. Griffiths. 2004. Leaf litter chemistry controls on decomposition of Pacific Northwest trees and woody shrubs. Can. J. For. Res. 34:2131-2146.
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
If you’re reading this, there’s an excellent chance that you have hair! Well, you’re not alone! Amazingly enough, many species of plants have “hair” too. Technically, plant hairs are called “trichomes” and they’re different from mammalian hair in many ways. They come in a variety of shapes and sizes, and perform many different functions. The plants at Tryon Creek State Natural Area (TCSNA) have a variety of different kinds of trichomes. Based on their physical properties, trichomes can protect plants from a variety of herbivores, reduce the loss of water and help spread the plant’s seeds.
Simple Plant Hairs
Let’s start out with the basic plant trichome. These simple trichomes can be found, for example, on the petiole (“petiole” is the little stem that attaches the leaf blade to the branch) of TCSNA’s own red elderberry (Sambucus racemosa L. var. racemosa), as shown below. These are simple, straight, unbranched hairs.
Plants, like most things in nature, are rarely frivolous. If they expend the energy to produce plant hairs, those hairs most likely have a purpose. One of the benefits of plant hairs is that they help reduce the rate of water loss from the plant. Imagine a water molecule trying to escape from the elderberry pictured above. The thicket of plant hairs on the stem dramatically slows down air movement right at the surface of the plant. This mass of plant hairs is essentially a maze that the escaping water molecules have to slowly wander through before it leaves the plant.
To demonstrate this effect, I set up the following demonstration. I took two small identical plastic tubs and completely filled them with water. The first tub (pictured below) is totally open to the atmosphere.
For the second tub, I inserted a scrub brush, bristle side up, into the top of the tub. The bristles of the brush created a maze similar to that created by plant hairs. The water molecules had to move through this maze in order to escape (evaporate) from the tub of water. And, yes, just like in plants, it did slightly reduce the open surface area of the water.
I weighed the containers as shown before the experiment started. After 36 hours of evaporation, I weighed the containers again. The open container lost 39 grams of water, while the “hairy” container lost only 25 grams of water, 64% as much as the open container.
Get a Grip!
Some of the trichomes found in the plant world are simple, but not straight. A good example found at TCSNA is the seed of the bedstraw (a.k.a. “cleaver”) plant (Galium spp.). The seed, which is shown below, is covered with stiff, curved trichomes.
In case you’re wondering why the seed has these hook-shaped hairs, take a look at the picture below.
The hook-shaped hairs allow the seeds to attach themselves to some innocent passing animal and hitch a ride to a new location. Presumably they will be brushed off, or rub off somewhere after the passing human or other animal has traveled some distance and “voilà” the plant spreads itself to a new growing place.
Plant hairs can defend against insects and other pests that want to eat the plants. Sometimes, the sheer density of the hairs can serve as a deterrent to hungry herbivores. Some insects might not be able to get through the hairs. Some larger herbivores might just experience the hairs as “sharp pokey things” and decide to leave the plant alone. A good example is the ultra-hairy seed of TCSNA’s bigleaf maple (Acer macrophyllum) as seen below.
Sometimes, defensive plant hairs are a little more complicated. One of the premier examples here at TCSNA is our beloved stinging nettle (Urtica dioica) which is pictured below. The stinging nettle uses some of its plant hairs defensively. The larger trichomes have a largely silica (like glass) hollow needle (blue arrow) mounted on a relatively soft green pedestal (red arrow) which contains toxins. When some animal carelessly brushes against it, the tip of the needle breaks off and the movement of the animal against the plant bends the needle over, squeezing the toxin out of the green tissue at the base of the needle. The toxin is thus injected into the offending animal. The toxins in this species include histamine, acetylcholine, serotonin, and formic acid. Typically they cause an itching sensation that for most people lasts no more than 24 hours. Note that the stinging nettle also has much smaller hairs (yellow arrow) that are common on many plants.
While humans tend to be very sensitive to stinging nettle, apparently it isn’t 100% effective against all animals. The banana slug (Ariolimax columbianus) pictured below crawling on stinging nettle seemed to be pretty calm and unconcerned by the trichomes. It may be that the slug is either immune to the chemicals in the stinging nettle, or its famous slime layer is protecting it or it moves so gently that it doesn’t break the nettle’s needles!
Human hairs are all unbranched. This is not necessarily so for plant hairs. The English Ivy (Hedera helix) has hairs that are branched. The pictures below show these branched hairs from two different perspectives.
Finally, there are glandular hairs, which produce chemicals in a small gland at the tip of the hair. One of the most interesting examples at TCSNA is the invasive plant commonly known as “herb Robert” (Geranium robertianum). Another name for this species is “stinky geranium.” If you ever pulled one of these plants, you’ll know why it’s called stinky geranium. On the tips of the hairs (blue arrow) on the stem below, you can see a small red dot. This red dot is actually a gland that produces the stinky chemical. One of the traditional ways humans have used the chemical produced by herb Robert was to rub it on their skin to repel mosquitos. It probably keeps insects away from the plant as well.
A second example of glandular hairs on a plant at TCSNA is hazel (Corylus spp.) Both of the hazel species that we have at the park have a significant number of glandular hairs, as shown in the photo below. The chemicals are located in the brown tips of the hairs. In both pictures below note that in addition to the glandular trichomes, the hazel also sports a large number of very small hairs on the midrib on the leaf.
Many interesting chemicals are produced by glandular hairs on plants. The trichomes of the sweet wormwood plant (Artemisia annua), which is not found at TCSNA, produce the chemical “artemisinin” which is an effective drug against malaria. And the psychoactive chemicals in marijuana (Cannabis sativa) are produced in the tips of the plant hairs of that species.
All in all, the hairs on plants are quite diverse, and have many functions. As has shown here, plant hairs can slow water loss, help spread the seeds to new locations, and protect the plant from herbivores. For the plants, the many functions of these trichomes do indeed make them a big hairy deal!