How Trees Work

Trees' general strategy as plants is to grow slowly, put a lot of time into building a structure that gets leaves closer to the sun, and eventually out-compete the fast-growing soft plants and shrubs that can't get off the ground.  The part that makes a tree a tree, namely the wooden trunk, serves as both support for holding up leaves and the means transportation of materials from the leaves to the roots and back. 

This is a tree.

 Tree trunks are strong because their cells have surrounded themselves with lignin, the hard material in wood.  There are two basic tissues in tree trunks: wood (the inside), and bark (the outside).  Guess which one of these materials is alive?  You'll have to wait just a minute to find out.  The wood part of a tree trunk contains mostly lignin, so it's very strong.  The bark contains more suberin and much less lignin.  Suberin, the subject of a previous post, is a softer substance, and if you have ever squeezed a wine cork, you know the texture of suberin.  Wine corks are cut from the bark of the cork oak. 

The wood of a tree is produced by plant cells growing very long, surrounding themselves with lignin,  leaving a few tiny holes in each end to connect to the next cells, then dying and leaving behind hollow tubes of lignin.  Yes, the interior of trees is mostly dead.  The hollow tubes connect down to the roots and up to the leaves.  The tubes are so narrow that water can pull itself up through the tubes by capillary action.  Capillary action occurs because water is pulled more by the chemical attractions of water to the lignin than by the pull of gravity.  Capillary action works in trees as long as the lignin tubes are very thin and the tree isn't too tall.  You may remember from 9th grade Biology that the material which transports water in plants is called xylem.  In fact, wood is almost entirely xylem.

Bark, the living part of a tree trunk, is composed of mostly phloem and suberin.  Phloem transports sugars, the tree's food, dissolved in water.  If you look at bark under a microscope, you would see that it, like wood, is composed of microscopic tubes running up and down the trunk.  Unlike xylem, phloem tubes can run up or down, depending on the season.  In the summer, the phloem is busy transporting extra sugars and nutrients down into the roots for winter storage.  In the early spring, phloem brings that stored sugar back up to provide energy for the new spring growth.

A tree will die if the bark is cut all the way around the tree.  The tree below has been girdled.  It is a white poplar, a weedy tree, that is probably interfering with the native plant restoration going on in Lincoln Park.  The ecosystem manager probably also applied an herbicide to the bottom cut on this girdle so it would be pulled down into the roots.  White poplars are notorious root-sprouters, and if you don't kill the roots, you will have new mini-trees coming up all over the place.

A girdled tree.

This tree has also been girdled, but not by humans.

A girdled green ash.

Bark is infinitely variable in its patterns and characteristics.  Here's my favorite bark - white birch.  You can tell a lot about a tree by looking carefully at its bark.  This will be the subject of a future post!

Beautiful birch bark.

Jellies at Shedd

We're in the middle of getting 6-8 inches of snow here in Chicago.  We've been putting off going to the museums until the winter weather really kicked in, and today was the perfect day to have an indoor adventure.  We spent a couple of hours at Shedd Aquarium, and we could have spent several more there.  My favorite exhibit was of the animals formerly known as jellyfish, currently known as jellies since they really don't have anything to do with fish other than the fact that they live in water.  I could watch them for hours - they are mesmerizing and fascinating.  Another museum-goer called them living lava lamps.

Northeast Pacific Sea Nettle, Chrysaora fruscescens

 I've written about jellies before, so I'll take a different approach here.  I'd like to point out some interesting anatomical structures and explain a little bit of their life cycle.  Let's start with anatomy.

The jellies above are swimming upside down.  The main body is called the bell.  There are two types of structures that trail behind the bell: tentacles and oral arms.  Tentacles are darker in the Pacific Sea Nettle, and they extend off of the edge of the bell.  Oral arms are usually whitish, four in number, and extend from the center of the bell.  Both appendages are covered in microscopic stingers.  The tentacles are for initial stinging of food and defense.  The oral arms are for more stinging and for moving food toward the center of the bell for digestion.

Jellies have only one orifice on their bodies, which has to serve for the in and out orifice of the digestive, reproductive and respiratory systems.  Food goes in, gets dissolved, is carried out through the rest of the body, and whatever isn't digestible is 'spit' back out.  Reproductive organs, visible as the four ring-shaped white structures in the moon jellies below, connect to the single orifice.  Males release sperm into the ocean water.  Females can release eggs into the ocean water, hopefully to find a sperm somewhere, or more commonly, they take in sperm, allow fertilization, and even allow development of the next generation inside their body cavities. 

Moon Jelly, Aurelia aurita

Jellies have a ring of muscle one-cell-thick around the edge of the bell that they can contract and relax to move.  Also around the edge of the bell, it is common for jellies to have light-detecting tissue for knowing when to swim up to the surface of the ocean.

Good view of the two types of appendages attached under the bell.

The jelly life cycle is pretty head-scratching.  The pictures on this page show all adult forms, but they have juvenile forms that look completely different - like butterflies and caterpillars look different.  Fertilized jelly eggs grow into larvae called planulae.  Planulae are almost microscopic and swim free in the ocean.  Some planulae can sting, and those invisible stings that sometimes get trapped inside your bathing suit could be planulae or they could be broken-off adult stingers.  Planulae swim to a hard surface, like a pebble or a rock, and they stick and grow into a polyp.  A polyp is a cup-shaped, usually transparent animal with tentacles in a ring around the top of the cup.  The bottom of the cup is stuck fast to a surface.  Polyps can grow mini-polyps off the side of themselves, which can fall off and become independent organisms (this is asexual reproduction by fragmentation).  Eventually, polyps grow a beret-like structure, let go of their substrate, and become an adult medusa to roam the ocean, sting at will, and reproduce the next generation.  Here is a nice diagram of the jellyfish life cycle.

Flower Hat Jelly, Olindias sp.

I'll end with a picture of an extremely strange jelly, the flower hat jelly.  It keeps its tentacles tucked up underneath its bell, and it extends them quickly when they are needed.  It is a benthic species, spending most of its time on the sea floor.  Those tentacles that extend off the top of the bell are mysterious, but I do know they are called exumbrella tentacles.  They might be lures to attract prey, or they could be stinging tentacles for self-defense.  If you are searching for a creature to study to make a name for yourself as a scientist, this might be a good subject, because little is known about it.

If you'll be in Chicago sometime in the next year, you're invited to come with me to the Shedd Aquarium - we have a membership!

Fun With Flamingos

I get a little taste of home when I walk through the Lincoln Park Zoo on my walking route because the zoo has flamingos.  Unlike Tennessee flamingos, these ones actually move and are not made of plastic.  I noticed them in October when the weather was nice, and I kept seeing the birds on my walks as the fall progressed.  I assumed they kept the birds out because the winter has been so mild thus far.  Well, yesterday I walked the zoo in 20 degree weather with sleety ice forming crusts all over every surface, and the flamingos were still out by their pond!  I realized there must be a few things I don't know about flamingos, so I did some research.

Tropical Paradise

 The Lincoln Park Zoo's flamingos are Chilean flamingos.  These birds survive high in the mountains of Chile where the temperatures can get down to -22 degrees F at night.  When the weather gets that cold, they stay near hot springs so they don't freeze solid, but these guys can handle some serious cold even without hot springs.

Flamingo with black flight feathers

 Flamingos' reddish coloration comes from carotinoid pigments in the food they eat, which is mainly red algae.  They filter the red algae out of wetland water, and they can feed in fresh to salty water, unusual for a land creature since salinity is so difficult to deal with.  Adults grow longer and stronger flying feathers that are black in color, and the displaying flamingo in the picture above is showing off his fine but clipped black flight feathers.

One of these is a flamingo.

 Flamingos are not born with a curved beak.  While it looks like they have run into a brick wall, flamingos' beaks actually turn down naturally as they begin to feed independently.  The downward curve allows them to filter algae out of the water.  Baby flamingos have a straight beak for sucking crop juice from their parents' throats.  Crop juice is a liquid that is nutritionally similar to mammal milk.  Both male and female adult flamingos make crop juice to feed their babies.  It is produced in an organ that is an offshoot of their digestive tract, and the parents hork it up to feed their little ones.  I don't know what sounds less appetizing - milk from glorified sweat glands like we have or regurgitated milk.  The best part about flamingo milk: it's RED!

Posing for the camera.

 Flamingos have red 'knees', but their 'knees' are actually ankles.  From those red bulges in the photo above down to the ground is all foot.  I should say, the bones below the red bulges are homologous to the foot bones in all other vertebrates with feet.  They have the same number and arrangement of bones in their feet as we do, but some of their bones are longer, shorter or fused or vestigial to make a flamingo foot.  Flamingos have true knees also, but they are too high to see and covered by feathers.  When flamingo legs bend, it appears they bend the wrong way, but when you take into account that the major joint in their legs is the ankle, they are bending the way any ankle bends.

Grooming seems to be a major activity.

 The flamingos at our zoo spend a large amount of time grooming themselves.  It's fascinating to watch because it reveals the musculature they must have to control their feathers.  The birds can raise some or all of their feathers with muscles that attach to the base of the feather under their skin.  They can willingly control these muscles so their feathers puff up or lay flat on demand.  Humans have similar muscles that connect to each hair, but they are not voluntary.  You can feel the muscles contract when the hair stands up on the back of your neck or when you get goose bumps.

More grooming with fluffed up feathers.

Salty Language

Chicago is beautiful all dressed up in snow, but after a couple of days, the look becomes pretty dingy.  The snow pushed aside by plows reveals its underside, gross from the street dirt.  The snert (snow + dirt) then melts into brown slush pools that look solid but give way when you step on them.  Dogs also decorate the snow as they are wont to do in our neighborhood.  Then there's the salt grime, white or a rainbow of colors, depending on what variety is used.

A salted bike path by the Navy Pier.

It's remarkable how much salt is applied on this city when it snows or ices.  The streets and sidewalks are quickly covered in the stuff.  It does indeed lower the freezing point of water to about 0 degrees Fahrenheit, enabling the snow and ice to melt and run off the sidewalk, so it's a useful substance when it's not extremely cold.  I can't help but wonder what happens to all that salt as it is washed off the sidewalks and down into the drains or soil. 

Salt has bounced off the sidewalk onto the soil above this tree's roots.

Even though life is thought to have originated in the ocean, where there is plenty of salt, life on land has adapted to a low-salt environment.  Land plants are very vulnerable to excess salt because their cells shrivel and break when exposed to salt water.  Try watering a houseplant with very salty water.  It will die.  If the houseplant is a flimsy, soft one, it will wilt and shrivel in a matter of hours.  The tree in the picture above is going to be very stressed in the spring when rain washes the salt down to its roots.  I imagine the city has to replace many trees and use salt-tolerant varieties as much as possible.  It is not uncommon to see screens erected around street-facing gardens to keep the salt out.

The salt that doesn't seep into the soil washes down into the storm drains.  Some storm drains probably go straight to Lake Michigan, but most go to a sewage treatment plant, thank goodness.  Urban storm runoff contains not just rainwater and salt, but everything that drips off the underside of cars, dog waste, pollution particulates that have settled out of the air, and countless cigarette butts.  It contains more toxic compounds than regular flushed sewage. 

Salt isn't usually removed during sewage treatment, and it is released back into the environment with the cleaned sewage water, usually into a river or lake.  The salt then raises the salinity of the river, increasing mortality for aquatic life.

Road salt is the same chemical as what you sprinkle on your eggs in the morning at breakfast: sodium chloride.  It is a necessary compound, and without any salt we would die.  For us here in North America though, too much salt is usually the problem for humans as well as urban soils and river life.  Salt causes problems in our bodies the same way it does for fish downstream from winter stormwater runoff.  It's essentially a water-balance issue.  Have you noticed how thirsty you get after eating a very high-salt food like Fritos or a cheeseburger or almost any meal at a chain restaurant?  That thirst is a symptom of salt imbalance.  The salt has dehydrated our cells just like it does for plants, and our bodies become thirsty, causing us to drink more water to dilute the salt and unshrivel our cells before they break.  The excess salt and water in our bodies causes swelling and a 1-3 pound increase in body weight (also known as water weight), until our kidneys can filter out the whole mess. 

People who eat a high-salt diet long-term maintain that swelling and high kidney workload for years.  It can, depending on one's genetics and other lifestyle factors, contribute to chronic high blood pressure and eventual strokes or cardiovascular problems.  The tiny capillaries in the body can be degraded from constantly having an elevated amount of fluid in them, which disrupts function in the extremities of the body, the brain, the kidneys, the heart, the eyes, and everywhere else capillaries are essential to body function (which is, really, everywhere).  Fortunately, salt is usually only found in such high quantities in processed food and restaurant food, so if you cook for yourself most of the time and just salt your food at the table, you should be OK.

Very large quantities of salt are toxic in the short term, also known as acutely toxic.  Salt toxicity by oral ingestion has been tested on mice (thankfully not on humans).  A dose of 4g of salt per 1 kg of mouse will kill 50% of mice within one day of ingestion (those numbers are called the LD50, or lethal dose for 50%).  If that number is applicable to humans, let's figure out what it means.  A typical 150 pound person weighs about 68 kg.  4g times 68 kg equals 272 g.  So 272 grams of salt gives a person 50/50 odds of survival.  272 grams is about 15 tablespoons.  Ick.  Hypernatremia (salt toxicity) symptoms of thirst, irritiability, weakness and dizzyness kick in way before coma and death, so the problem can be remedied before it gets too bad.  Hypernatremia in humans is actually more commonly caused by removing water instead of adding salt, and we refer to it as dehydration.

Bacteria and other microbes are killed by excess salt the same way our cells are.  The salt causes their cells to shrivel.  Humans have taken advantage of this trait and used salt to prevent microbes from surviving on some foods and spoiling them.  Beef jerky, for example, is "cured" with lots of salt.  You can demonstrate this phenomenon by taking a piece of beef jerky and a piece of raw steak and leaving both out on the counter in your kitchen for a week.  Be sure to check on them daily to notice any smells or discoloration.  Or flies.

Now back to snow.  Seattle has decided it doesn't want to deal with salt pollution problems, and they handle snow clearing in a different way.  Seattle plows the snow with a rubber-coated plow, leaving some snow in a hard-pack on the streets.  Then they sprinkle sand on top of that.  The surface becomes less slippery, and the sand helps cars grip.  The streets are passable for front-wheel drive vehicles and all-wheel-drive vehicles, but they are tricky for rear-wheel-drive cars, such as the police use (oops).  Even though this solution has a slight logistical cost for getting around in winter, it really cuts down on the costs of environmental damage to Puget Sound.  Salt run-off harms fishing and tourism industries in the sound by reducing aquatic life, and it also slows natural nutrient cycling by killing bacteria, so the sound doesn't stay clean.  Seattle-ites would rather have a clean Puget Sound and drive a little slower in the winter.

Alders

I have seen so many things in Chicago that I had only previously known from reading about them: Lake Michigan, excellent public transit, Chinese steamed buns, earlobe loops that stretch all the way to the shoulders.  My second favorite (after public transit) is a tree I have always admired: the alder (here you can see the leaves, which aren't available this time of year in Chicago).

Alders are in a fine plant family, the Betulaceae, or birch family.  Birches are marvelous trees despite their small stature.  They have nicely-shaped rounded but toothed leaves, a branched and clustered growth form, and that great bark that you have to resist peeling if you don't want to kill the tree.  In fact, I like birches so well, I named my dog Birch (Botany nerd joke: his Latin name was Betula tomentosa var. lutea).

Alders have all those great characteristics except the peeling bark, but they also happen to have flowering structures that reveal an important evolutionary link.  Remember learning in 4th grade that there are two kinds of trees, evergreen and deciduous?  This distinction divides trees into the two main groups of all plants (except those weird and ancient-looking mosses, liverworts, ferns, and the fern allies).  The two main groups of plants are Angiosperms and Gymnosperms.

Angiosperms all have some type of flower, including those plants with bright, gorgeous flowers, like the tulips and those with small, dull flowers like grasses and oak trees.  Deciduous trees are Angiosperms (though a few Gymnosperms do technically lose their leaves).  Another characteristic of Angiosperms is that they produce seeds inside fruits. I'm using the botanical definition of fruit here, meaning a hard or fleshy container  around a seed, like an apple, tomato, walnut shell or pumpkin.  The term Angiosperm refers to this phenomenon of having seeds enclosed within a structure (angio = enclosed, sperm = seed).

Gymnosperms produce seeds but don't bother to wrap them in anything.  The prefix, gymno-, means naked, which kind of makes you wonder about the word gymnasium.  Gymnosperms  produce seeds in cones, but the cones do not enclose the seeds.  The naked seeds just fall right out of those cones when they are ready to germinate.  Most Gymnosperms are trees, and most of those have needle-like leaves that are evergreen and do not fall in the Fall.

I was really desperate for a picture of a cone here.  Glitter is not natural on cones.

Cones are plant organs with repeated flat things called scales. The cones are either male or female, and their scales produce either pollen (plants sperm) or ovules.  Wind blows the pollen to the ovules, and then the fertilized ovule grows into a seed.  The big cones like the ones pictured above are female cones.  Male cones look a little bit like those strange brown mini corn cobs you sometimes get in Chinese food.  The evolution of Angiosperms from Gymnosperms included the flattening and softening of the cones' scales along with production of pigments and scents.  Flowers are basically cones modified to attract insects for carrying pollen from male to female plant structures.

Alders (I haven't forgotten we're actually talking about alders here) are Angiosperms with flowers that look remarkably like cones.  The entire Betulaceae family evolved from an evolutionary bridge group of plants that maintained more ancestral gymnosperm-like characteristics in its pollen and ovule-producing structures.  So alders are modern, flowering plants that produce seeds in fruits, but they have flowers that look just like the cones from their evolutionary ancestors.

Alder flowers look just like cones!