Reflections on Hope Jahren’s Lab Girl

After the spring 2020 tribulations with hits and misses in my seed trays, the words by Hope Jahren on seeds was profoundly moving and reassuring.

Somehow I felt vindicated for having faith that some of the older seeds just might spring to life, and also let off the hook for those who didn’t.

A seed knows how to wait.  Most seeds wait for at least a year before starting to grow; a cherry seed can wait for a hundred years with no problem.  What exactly each seed is waiting for is known only to that seed.  Some unique trigger-combination of temperature-moisture-light and many other things is required to convince a seed to jump off the deep end and take its chance – to take its one and only chance to grow.

A seed is alive while it waits. Every acorn on the ground is just as alive as the three-hundred-year-old oak tree that towers over it.  Neither the seed nor the old oak is growing; they are both just waiting.  Their waiting differs, however, in that the seed is waiting to flourish while the tree is only waiting to die.  When you go into a forest you probably tend to look up at the plants that have grown so much taller than you ever could.  You probably don’t look down, where just beneath your single footprint sit hundreds of seeds, each one alive and waiting.  They hope against hope for an opportunity that will probably never come.  More than half of these seeds will [p.38] die before they feel the trigger that they are waiting for, and during awful years year every single one of them will die.  All this death hardly matters, because the single birch tree towering over you produces at least a quarter of a million new seeds every single year.  When you are in the forest, for every tree that you see, there are at least a hundred more trees waiting in the soil, alive and fervently wishing to be.

A coconut is a seed that’s as big as your head.  It can float from the coast of Africa across the entire Atlantic Ocean and then take root and grow on a Caribbean island.  In contrast, orchid seeds are tiny: one million of them put together add up to the weight of a single paper clip.  Big or small, most of every seed is actually just food to sustain awaiting embryo.  The embryo is a collection of only a few hundred cells, but it is a working blueprint for a real plant with root and shoot already formed.

When the embryo within a seed starts to grow, it basically just stretches out of its doubled-over waiting posture, elongating into official ownership of the form that it assumed years ago.  The hard coat that surrounds a peach pit, a sesame or mustard seed, or a walnut’s shell mostly exists to prevent this expansion.  In the laboratory, we simply scratch the hard coat and add a little water and it’s enough to make almost any seed grow.  I must have cracked thousands of seeds over the year, and yet the next day’s green never fails to amaze me.  Something so hard can be so easy if you just have a little help.  In the right place, under the right conditions, you can finally stretch out into what you’re supposed to be.

After scientists broke open the coat of a lotus seed (Nelumbo nucifera) and coddled the embryo into growth, they [p.39] kept the empty husk.  When they radiocarbon-dated this discarded outer shell, they discovered that their seedling had been waiting for them within a peat bog in China for no less than two thousand years.  This tiny seed had stubbornly kept up the hope of its own future while entire human civilizations rose and fell.  And then one day this little plant’s yearning finally burst forth within a laboratory.  I wonder where it is right now.

Each beginning is the end of a waiting.  We are each given exactly one chance to be.  Each of us is both impossible and inevitable.   Every replete tree was first a seed that waited.

(This is the entirety of Lab Girl, chapter 3, pp 37-39.)

Her exploration of roots is equally exquisite.

No risk is more terrifying than that taken by the first root.  A lucky root will eventually find water, but its first job is to anchor – to anchor an embryo and forever end its mobile phase, however passive that mobility was.  Once the first root is extended, the plant will never again enjoy any hope (however feeble) of relocating to a place less cold, less dry, less dangerous.  Indeed, it will face frost, drought, and greedy jaws without any possibility of flight.  The tiny rootlet has only one chance to guess what the future years, decades – even centuries – will bring to the patch of soil where it sits.  It assesses the light and humidity of the moment, refers to its programming, and quite literally takes the plunge.

Everything is risked in that one moment when the first cells (the ‘hypocotyl’) advance from the seed coat. The root grows down before the shoot grows up, and so there is no possibility for green tissue to make new food for several days or even weeks.  Rooting exhausts the very last reserves of the [p.68] seed.  The gamble is everything, and losing means death.  The odds are more than a million to one against success.

But when it wins, it wins big.  If a root finds what it needs, it bulks into a taproot – an anchor that can swell and split bedrock, and move gallons of water daily for years, much more efficiently than any mechanical pump yet invented by man.  The taproot sends out lateral roots that intertwine with those of the plant next to it, capable of signalling danger, similar to the way that information passes between neurons via their synapses.  The surface area of this root system is easily one hundred times greater than that of all the leaves put together.  Tear apart everything aboveground – everything – and most plants can still grow rebelliously back from just one intact root.  More than once.  More than twice.  (Excerpt from Chapter 5 of Lab Girl, pp 67-68)

And this, on leaves.

The first real leaf is a new idea.  As soon as a seed is anchored, its priorities shift and it redirects all its energy toward stretching up.  Its reserves have nearly run out and it desperately needs to capture light in order to fuel the process that keeps it alive.  As the tiniest plant in the forest, it has to work harder than everything above it, all the while enduring a misery of shade.

Folded within the embryo are the cotyledons: two tiny ready-made leaflets, inflatable for temporary use. They are as small and insufficient as the spare tire that is not intended to take you any farther than the nearest gas station.  Once expanded with sap, these barely green cotyledons start up photosynthesis like an old car on a bitter winter morning.  Crudely designed, they limp the whole plant along until it can undertake the construction of a true leaf, a real leaf.  Once the plant is ready for a real leaf, the temporary cotyledons wither and are shed; they look nothing like all the other leaves that the plant will grow from this point forward.  [p82]

The first real leaf is built using only a vague genetic pattern with nearly endless room for improvisation.  Close your eyes and think of the points of a holly leaf, the star of a maple leaf, a heart-shaped ivy leaf, a triangular fern frond, the fingery leaves of a palm.  Consider that there can easily be a hundred thousand lobed leaves on a single oak tree and that no two of them are exactly the same; in fact, some are easily twice as big as others.  Every oak leaf on Earth is a unique embellishment of a single rough and incomplete blueprint.

The leaves of the world comprise countless billion elaborations of a single, simple machine designed for one job only – a job upon which hinges humankind.  Leaves make sugar.  Plants are the only things in the universe that can make sugar out of nonliving inorganic matter.   All the sugar that you have ever eaten was first made within a leaf.  Without constant supply of glucose to your brain, you will die.  Period. Under duress, your liver can make glucose out of protein or fat – but that protein or fat was originally constructed from a plant sugar within some other animal.  It’s inescapable: at this very moment, within the synapses of your brain, leaves are fueling  (sic) thoughts of leaves.

A leaf is a platter of pigment strung with vascular lace.  Veins bring water from the soil to the leaf, where it is torn apart using light.  The energy produced from this tearing apart of water is what glues sugars together after they are fixed from the air.  A second set of veins transports the sugary sap out of the leaf, down to the roots, where it is stored and packaged for either immediate or longer-term storage.

A leaf grows by enlarging the string of cells located along a central vein; single cells on the perimeter eventually decide [p83] independently when to stop dividing.  From this tip, smaller veins develop, eventually completing the network at the stem; thus the overall maturation proceeds from tip to base.  Once the most daring portion of the leaf is complete, the plant puts horse before cart and begins to slide sugar back down and in, down to where it will be used to make more root, which will be used to bring up more water, which will be used to expand new leaves, which will pull back more sugar, and in this manner four hundred million years have passed.

Of plants in general, she writes in chapter 9:

Every plant can be separated into three components: leaf, stem, and root.  Every stem functions the same way: as a bundle of bound straws, bales of microscopic conduits that carry soilwater up out of the roots and sugary-water down out of the leaves.  Trees are a unique type of plant because their stems can be more than one hundred yards long and are made of this amazing substance that we call wood.

Wood is strong, light, flexible, nontoxic, and weather-resistant; thousands of years of human civilization have yet to produce a better multipurpose building material.   Inch for inch, a wooden beam is as strong as one made from cast iron but is ten times more flexible and only one-tenth as heavy.  Even in this age of high-tech man-made objects, our preferred construction material for housing remains lumber hewn from trees.  In the United States alone, the total length of the wooden planks used during the last twenty years was more than enough to build a footbridge from the planet Earth to the planet Mars. [p.100]

People slice up tree trunks, nail the pieces together into boxy shapes, and then go inside to sleep.  Trees use the wood in their trunks for a different purpose – namely, the use it to fight with other plants.  From dandelions to daffodils, from ferns to figs, from potatoes to pine trees – every plant growing on land is striving toward two prizes: light, which comes from above, and water, which comes from below.  Any contest between two plants can be decided in one move, when the winner simultaneously reaches higher and digs deeper than the loser.  Consider the tremendous advantage that wood confers to one of the contestants during such a battle: armed with a stiff-yet-flexible, strong-yet-light prop that separates and connects – leaves and roots, trees have dominated the tournament for more than four hundred million years.

Wood is a static, utilitarian compound, constructed once and left to stand as inert tissue forevermore.  From the tree’s center (or ‘heartwood’) radiates a network of ray cells that bring cool xylem and sweet phloem to the cambium layer on the periphery.  The cambium layer manufactures the living sheath that rests just below the bark.  A tree grows by producing one new sheath after another.  When a sheath is outgrown, its woody skeleton is left behind, progressively forming the rings that we can see in cross section after a tree is felled.

A tree’s wood is also its memoir: we can count the rings to learn the tree’s age, for every season of growth requires a new sheath from the cambium.  There’s a lot of additional information written into tree rings, but it is coded within a language that scientists don’t speak fluently – yet.  An unusually thick ring could signify a good year, with lots of growth, or it [p.101] could just be the product of adolescence, a random spurt of growth hormones cued by an influx of unfamiliar pollen from a distant source.  A ring that is thick on one side of the tree but thin on the other tells the story of a fallen branch.  When a branch is lost, it upsets the balance of the tree, triggering cells within the trunk to reinforce the side that must now support the newly uneven burden of the crown.

For trees, losing limbs is the rule, not the exception.