There is light everywhere.  The sky is blinding-blue infinity. The snow draped across The Garden is as brilliant as  cut glass and gemstones. 

Twigs shimmer and glint like daggers flashing with flames. But it is really cold out this morning, somewhere around 10 F. With each of my steps, the snow squeaks underfoot. The air is dry as sandpaper and scrapes across my lips as I inhale.  Today is a contradiction in fire and ice.

“Crunch, crunch,” say my steps.  I pretend I’m not freezing, because the long dark is over and it’s a great day to prowl The Garden.

Our rhododendrons (Rhododendron cvs.) in The Japanese Garden look especially cold.  The leaves have pointed their tips toward the ground, and tightly curled themselves into green cigars. They’re huddling against the cold, in an effort to minimize evaporative water loss to the desiccated air.  When it warms up, the leaves will un-curl and stand up again.  They accomplish this directionless, or nastic, movement by draining and filling specialized elastic, temperature-sensitive motor cells, which pull the leaves along with them as they change shape.

Contrast nastic movement with tropic plant movements, where plants respond to stimuli by moving toward or away from their particular nudge.  Phototropism (light), gravitropism (gravity), thigmotropism (touch), and geotropism (earth) move leaves, stems and roots the directions they need to go. Their mechanisms are diverse, often complicated, and always fascinating; I’d like to promise more of this in a later blog. So, let’s not even mention animal and wind mediated movements, which make plants world travelers.

The little grove of hemlocks (Tsuga canadensis) just across the brook seems more obviously content with the cold.  Like the rhododendrons they are evergreen plants, but they employ another winter survival strategy.  First, their leaves are very tiny to limit surface area, and thus evaporative loss.  Second, their leaves are coated with a thick, resinous cuticle, which waterproofs just like the paraffin painted on our grocery-store rutabagas lately. Third, hemlock leaves have no pores on their upper surfaces, and only two rows on their undersides, those being nestled up against the mid-veins.

Fifty paces away, in the shade of the Woodland Garden hillside, a non-woody evergreen hides in the snow, the Christmas fern (Polystichum acrostichoides).  I brush away some frost crystals, and there they are, clad in olive drab, waiting for April. They’re common in Ohio woods, and on days like this appear cheery and gay, climbing our ravines in little green armies.

With the frozen earth preventing water uptake, it is impossible for Christmas ferns to photosynthesize today.  So they wait, green and ready.  Plants that keep their leaves through the winter use a couple techniques to prevent living cells from freezing and bursting.  They move intracellular water just outside of their cells walls, where it safely freezes. This simultaneously concentrates the dissolved carbohydrate inside the cell, which then acts as antifreeze.  Green-in-winter plants also employ antifreeze proteins that bind water molecules and prevent them from crystallizing.

I make an about-face, toward the big tulip tree (Liriodendron tulipifera) growing in the Woodland Garden.  Seventy-five feet above me its top branches bend and angle and stay substantial out to their twig-tips.  They are bearing erect seed clusters that glow orange in the light, and look like hundreds of sky candles burning to warm the frozen sun.  The individual seeds are spindled around central pins, and are upright and clasping like folded umbrellas.  The seeds not eaten by fox squirrels will break free one-by-one and flutter away on little wings.  All will be down by spring, leaving just the pins on the branches.

Fighting by not fighting, the tulip threw its leaves to the ground and drained its sap to the roots last autumn.  It stands today, visibly dormant and indifferent to winter…but not quite.  The mitten-shaped buds hold some living cells, quiet but alive, that wait beneath the protection of woody scales.  Come spring, they will burn stored starches pumped from below, grow out of their cocoons, and become summer’s leaves.

Fire and ice in the Gardens.  So beautiful, but I’m goin’ inside now—“crunch, crunch”–man, its cold out here.

Posted by Mark Bir

Tags: cleveland botanical garden, hemlock, Mark Bir, nastic movement, plant antifreeze proteins, rhododendron, tulip tree, winter trees

This entry was posted on Sunday, February 7th, 2010 at 2:12 pm and is filed under Mark Bir, Trees and Shrubs, Winter Gardening. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.