Monday, May 13, 2013

Ferns Unfurling into the Future

Since spring is the time of transition, this blog is transitioning too.  It is time for my final outdoor classroom blog post.  Next time, I will return to my original "Biological Thinking" blog of discovering biological phenomena in everyday encounters with nature.  I hope you stay tuned if you have enjoyed my site-specific posts.  Thank you for reading!
A Fern Leaf
Our final topic: ferns.  Ferns are so common in the South that it is easy to overlook their strange beauty.  In the summer, many people display ferns in baskets outside their homes or apartments.  If you walk through the woods, ferns contribute to much of the background green of the understory.  Their repetitive intricate form makes them ideal for adding greenery to bouquets.  They are so familiar, yet they are so unusual. 
Fern spore-producing structures called sporangia.
Most plants we know of produce flowers and seeds to grow their offspring.  Seeds are tiny plants with a starter food supply wrapped in a protective coating.  They are produced from flowers.  When a seed grows, the tiny plant in it gets larger until it is a hackberry tree or a clover plant or, well, you get the idea.  Ferns, however, do not make flowers or seeds.  Fern plants make spores.  Spores are microscopic bits that are so light they can blow for miles on the wind.  When they land, if conditions are moist, they can grow into a small green leaf-like flat structure called a gametophyte.  The gametophyte looks nothing like a fern - just a tiny green patch.  The gametophyte grows for a while on its own, then it produces structures that can grow into a full-grown fern.

It's difficult to find gametophytes, but its easy to find spores.  Just look for dots on the bottom sides of fern leaves - those are pockets filled with microscopic spring-loaded spore-launchers called sporangia.  If you could shrink yourself, you could hang out under a fern leaf just for the fun of watching the tiny sporangia catapult their spores.  Nature's microscopic fireworks!
How leaves of flowering plants open up.

Another difference between ferns and flowering plants is how their new leaves open up.  The above plant, a flowering plant, has new leaves that are enlarging and opening by unfolding.  The young leaves are small and creased, the mature leaves are open and flat.  Below you see a fern leaf opening up.  Young fern leaves are small and curled up.  When they grow, they unfurl or unroll.  Young fern leaves look like the tops of violins (also called fiddles), so young fern leaves are called fiddleheads.  Fiddleheads might be green or brown or hairy or look quite different than the leaves they mature into.  It's easy to find fiddle heads in the spring and early summer - just look around the base of fern leaves, which we have in abundance all over our outdoor classroom.
Fern fiddlehead with a spore-producing leaf behind it.
There is a term for the unfurling of fiddleheads, of course, since there is a term for everything in science.  It is perhaps my favorite scientific term: circinate vernation (pronounced SIR-sun-ate ver-NAY-shun).  Look at the first word: circinate.  What other word starts with circ-?  Circle!  Circinate means circling or spiraling.  The second word might be tougher to figure out.  It derives from the word 'vernal', which means spring.  So circinate vernation is literally the unfurling of the spring, which is what ferns do.
More fern fiddleheads.
Ferns are ancient plants on earth.  Well, the plants in our outdoor classroom plant beds aren't ancient - they are the same age as their flowering neighbor herbs.  What I mean is that ferns were present on earth before flowering plants evolved.  They were some of the earliest plants in the fossil record, and they used to be the dominant type of plant on earth.  Now ferns are all fairly small plants, but before there were trees like we have now, ferns could be any size up to as large as small trees.  Ferns spores are a limitation that requires moist habitat, so ferns can't grow everywhere.  When some plants evolved the ability to form flowers and seeds, they could live in many types of habitats, so the flowering plants out-competed the ferns and became the dominant types of plants on earth. 
This fern leaf is almost completely unfurled.
All plants, including ferns, use photosynthesis to capture the sun's energy and make food.  Like flowering plants, ferns have xylem and phloem vessels for transporting food and water.  There are even more simple and ancient plants still easily found, even in our outdoor classroom: the mosses.  Take a look at the plants covering the rocks behind with waterfall.  They are mostly mosses, which don't have flowers, seeds, xylem or phloem.  They still photosynthesize, and they make spores like ferns do.
Moss - an even simpler plant than ferns.
If you want a more ancient plant than moss, you have to look into the pond at the algae.  Which brings us back to the very first topic we started with in August! 

I will leave you with one last picture of a fiddlehead getting ready to open up and live its life in the world.  It's so full of possibility!
A young fiddlehead.





Thursday, May 2, 2013

Hello! I'm Veronica. I'll Be Your Nectar Guide Today

The plant below is called Veronica.  That's its scientific name and its common name.  In our outdoor classroom, it's located on the rocks behind the pond, and it's blooming like crazy right now.  Veronica flowers have something really neat called nectar guides. 

Nectar Guides on Veronica Flowers

Nectar guides help bees find flowers.  They point to the part of the flower that contains the nectar, which is what bees are looking for.  Nectar is sugary plant sap found in the base of many flowers, and it is perfect bee food.  I like to think of nectar guides working a lot like the stripes and lights on airport runways telling airplane pilots where to land their planes.

Why would flowers advertise where their nectar is?  It turns out flowers are offering the nectar in a bargain.  Do you see those tiny white structures poking out of the flowers in the picture above?  Those are anthers, and they contain a dust called pollen.  Flowers must have pollen moved from one flower to another in order to be able to grow seeds to grow a new generation.  While a bee sips the nectar in a flower, those anthers are in the perfect place to dab some powdery pollen onto the bee.  Then the bee rubs off the pollen at the next flower it goes to.  The flowers are giving the bees a meal in return for moving their pollen from one place to another.  (Do you remember the name for a close relationship between two organisms where both organisms benefit?  The answer is at the bottom of this page.)

Bee-pollinated flowers usually have nectar guides.  Flowers that are small, fragrant and with a shallow cup for nectar are usually bee-pollinated, and we have lots of bee-pollinated plants at our outdoor classroom to discover.  You may not always notice nectar guides on bee flowers because sometimes the guides are invisible to human eyes.  Strangely enough, there are more colors of light than humans can see.  Rainbows actually have more stripes than humans see, in colors we haven't imagined.  Bees can probably see one more stripe on the rainbow than we can.  We call this color ultraviolet, and know it exists because we can detect ultraviolet with machines.  But how do we know bees can see ultraviolet?  Because scientists have given bees eye tests!  Scientists tested bees' eyesight by making fake flowers.  On some flowers, they painted nectar guides with an ultraviolet dye.  When you offer fake flowers to bees, the bees are way more curious about the ones with the ultraviolet nectar guides than the ones without nectar guides.  Scientists have detected ultraviolet nectar guides on real flowers (sunflowers have ultraviolet nectar guides).

Go back to the picture above and see if you can find the nectar thief.  A nectar thief is something that steals nectar without moving pollen - a parasite!  The nectar thief on our Veronica flowers is an ant toward the left of the picture.  As we learned last week, ants eat sugar, so it's no surprise that they would like flower nectar.  The ants are too small for the anthers to dust them with pollen, so they slip in, drink the nectar and slip out again without helping the plant.  Ants mostly use smell and taste to find their way in the world, so they probably don't even notice the nectar guides.  If you are jealous of bees for seeing one more color than we do, then you're really going to be mad at ants.  Scientists think ants can smell and taste an enormous number of things humans can't, with much more precision.  If you don't believe me, try closing your eyes and finding your way around using just your nose and tongue, and you will appreciate just how much better ants' senses are.

Answer: Mutualism