Diaspora

Diaspora is a Greek word meaning the scattering of seeds. We are now heading into late summer and plants are setting seed. One of the things I most enjoy at this time of year is marveling at the variety of forms produced by seed bearing plants.

Seeds hold an embryo and carry the genetic material of a new plant. There are three methods evolved by plants to disperse their seeds-by wind, by water, and by animals.

The structures used by plants to get their seeds aloft and carried by the air currents of the earth are masterpieces of engineering. The designs include gliders, parachutes, whirlybirds, and spinners. Gliding seeds are said to have inspired the designs of some early aircraft. I like to think that spinner or whirlybird seeds may have contributed to one of Leonardo Da Vinci's concepts for a flying machine.

An outstanding example of the parachute design is the ubiquitous Common Dandelion (Taraxacum officinale) a member of the Composite family. The seed (achene) is attached by a thin stalk to a radiating plume of bristly hairs (pappus). So equipped, the seeds become airborne in response to the slightest breeze. As is often the case with parachuting seeds, they are arranged in a globular puff. Another name for the dandelion is blowball. The word pappus is Latin for old man.

The Composite family includes sunflowers, daisies, coneflowers, chicory, and thistles. In members of this family, the pappus is modified in a multitude of ways, often to promote the effective dissemination of seeds. For example, in sticktights, the pappus is barbed so that it adheres to passing animals. The characteristic of the pappus is important in identifying the particular species of a Composite blossom.

In his last years, Thoreau was working on an exhaustive research project to determine all of the dominant patterns of seed dispersal within an hour's walk of his home in Concord, Massachusetts. He called it "learning the language of the fields." Thoreau was one of the first American field ecologists to apply Darwin's ideas of natural selection to the subject.

Thoreau died from a respiratory infection before he could finish his manuscript entitled The Dispersion of Seeds. The work is an argument against the then-prevalent theory that some plants grew spontaneously without any root, seed, or cutting from a parent plant. Typically, Thoreau combines keen observation with a view to a larger perspective. His description of the milkweed ends with these thoughts :

I am interested in the fate or success of every such venture which the autumn sends forth. And for this end these silken streamers have been perfecting themselves all summer, snugly packed in this light chest, as perfect adaptations to this end--a prophecy not only of the fall, but of future springs...Who could believe in prophecies...that the world would end this summer, while one milkweed with faith matured its seeds?

Alphabet Bloggers

Reading Thoreau and Edwin Way Teale. How thrilling to feel we are communing across the decades when I observe something of nature, try to describe my perceptions in words, then shortly thereafter read what they have written in the same vein that validates my experience.
On a birding outing on the Potomac recently I saw a young eagle fly overhead, and described its "princely glide" to capture its seemingly self assured and stately motion. Teale referred to sighting an eagle gliding back and forth in a manner so steady "it appeared as if riding on rails." On the same trip I spotted the facing silhouette of a bluebird perched in a faroff canopy, but couldn't identify it without using my glasses to see the blush breast and blue wings. Teale wrote of the bluebird's "round shouldered" attitude which was spot-on with what I saw. Next time I'll recognize it without my glasses! (Field glasses, that is, I will still need my prescription lenses or contacs!)
Reading "Walking" last night Thoreau comments on seeing ducks on the water in spring. First he "saw one bird, then suddenly there were three." That is exactly what occurred when I saw the Hooded Mergansers on the Shenandoah. One bird was visible since the other three were diving unbeknownst to me. I glanced down to raise my glasses, the divers had surfaced! It is reassuring to know these writers whom I revere saw and appreciated the same animal behaviors that are available for me to witness and enjoy.