Monday, November 10, 2014

Pine Seed Saga

When I'm pining for a naturalist adventure, I don't jet to an exotic locale, I zoom in for a closer look at a common animal or plant. As naturalist E.O. Wilson observed, “A lifetime can be spent in a Magellanic voyage around the trunk of a single tree.”


Recently, I collected a cone from beneath a neighborhood grove of Eastern White Pine (Pinus strobus). Tagged the Sequoia of the east, this species can live more than 450 years and achieve heights of over 150 feet. Tall, straight, and lightweight, the trunks of White Pine were once in great demand for the masts of sailing ships.


Vast virgin stands were decimated, but White Pine has been widely replanted for lumber, windbreaks and privacy screening.  The tree also provides a variety of wildlife with food and cover. Bald eagles often choose a white pine's lofty crown for their nest.


Pine needles grow in bundles called fasicles. White Pine is the only native eastern pine with five-needled fasicles equating to the five letters of its name. A mature White Pine cone is also distinctive, usually between 3 and 6 inches long and one to two inches thick, with a long slender peduncle, or stem.  


In all my casual encounters with pine cones, I realized I had never seen a pine seed and wasn't even sure exactly what to look for.  My cone's scales arched dramatically outward from the central axis, but at first glance I saw nothing resembling a seed.  I tried covering the cone with a dish towel and twisting back and forth with both hands.


The seeds that dropped out were suprisingly delicate--each consisted of a translucent wing about 3/4 of an inch long narrowing to a tiny brown pellet, about the size of broken pencil point. Viewed under my dissecting microscope, the surface of the wing suggested the hide of some fantastic animal.  Iridescent striations incorporating loops and whorls ran its length, continuing over the almond-shaped structure that enclosed the seed.


Using an instrument, I was able to halve the miniscule seed to view the interior. Within was a soft white meaty substance surrounding a yellowish inner core.  For comparison, I sliced open a much larger pine "nut" (the seed of the Pinon Pine, a western species) and saw the same arrangement but in more detail.  The core resembled a sturdy trunk with short appendages on one end.


White Pines, like all conifers, produce both male and female cones. The male cones look like miniature corn cobs,  and grow in upright bunches.  They wither and fall off the tree after releasing clouds of golden pollen between April and June.


This wasteful abundance is necessary since pine pollination is dependent on the wind, unaided by bees or other creatures. Each pollen grain has an ear-like parachute on either side to increase the odds of it reaching its destination: the ovule within the scales of a female cone.


Immature female cones are also quite small and usually go unnoticed as they emerge on the higher branches. Their tender green scales part to receive the pollen, ideally from a neighboring tree. Each scale then closes to develop a pair of seeds.  By early fall of the second year after pollination, the cone has enlarged to become the brown, woody object with which we are familiar. The seeds are ripe but the scales reopen to release the seeds only when conditions are dry.


With a good breeze in an open landscape, the propeller-like wings can lift and spin the seeds up to 700 feet from the parent tree.  Each seed carries a miniature seedling, an embryo with needles, roots and stem, nestled within a supply of nutrients for initial growth. 


By the time a female cone drops from the tree, most of the seeds have already fallen or blown away. Gray squirrels, mice and voles also aid in dispersal when they cache pine seeds and fail to consume them all.

Pines--like cedars, hemlocks, spruces and most other familiar evergreens--are conifers (cone bearers). Conifers descend from the 300 million year-old lineage of non-fruiting plants, classified as gymnosperms (meaning naked seeds).  Gymnosperms have survived geologic upheavals, climate change, major extinction events, and the formidable competition of the angiosperms, the flowering plants.

Today's conifer families are ancient--all had evolved by the end of the Jurassic 150 million years ago. When dinosaurs reigned, conifers dominated the plant world.

Paleobotanist Andrew Leslie of Yale University, studying the fossil record, determined that female cones first bulked up during this period of co-existence.


Leslie theorizes that this adaptation was a response to the immense appetites of herbivorous long-necked sauropods such as Diplodicus (90 feet long). Other scientists point out that the rise of small mammals, birds and even insects may have had an influence.


I will never look at a pine cone the same way again.

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