As October ages, Nature changes gears. In the plant world, the final flowers senesce, their colors replaced by objects that are much more drab, but even more remarkable. We’ve entered seed season.
The primary purpose of seeds, of course, is reproduction. From the plant’s perspective, a seed represents a substantial investment of resources by an individual plant, made so that the species as a whole will survive. Depending on your perspective, this process is either remarkably effective or a woeful exercise in inefficiency.
On the positive side, seeds generally get the job done. Plant species persist, spread, move, and over the very long term, evolve by means of their seeds. The sheer abundance and diversity of plant life argues that this process works well.
Each seed contains the beginning of a new plant, a few cells formed from the union of male genes, carried on pollen grains, with ovaries, or the female parts of flowers. Almost invariably, seeds also contain stored energy in the form of carbohydrates or oils, a little reserve of energy and nutrition to help a new sprout get started. Also universal are structures to protect the nascent plant and its stash of energy: To one degree or another, seeds are generally enclosed in hard and weather-resistant shells that guard against foraging insects, too much or too little moisture, or abrasion.
Moreover, many types of seeds are equipped with features aimed at dispersal. Plants, of course, are literally rooted in place, and it is generally through their seeds that they explore and colonize new locations. The strategies are many and varied. Some species of violets, for example, produce seeds coated in sugar, encouraging ants to collect them as food and thereby drag the seeds across the landscape.
Jewelweed, sometimes known as touch-me-not, produces spring-loaded seed pods that burst upon the lightest touch when fully mature, launching seeds on trajectories that may take them several feet from their source. It doesn’t sound like much, but over generations, this dispersal method lets a stand of jewelweed move to remain in salubrious conditions. Many other plants, most famously the milkweeds, take to the air on ethereal tufts of fiber. On a warm and calm autumn day, you can toss a milkweed seed into the air and watch it rise out of sight on a column of ascending heated air. Who knows where it will end up?
Packaged in their resistant coating, seeds can persist for an amazingly long time, waiting for the right conditions to sprout. Clear a Vineyard woodlot, and meadow flowers often pop up, taking advantage of an ecological change that they have waited patiently for across decades. For some plants, a long latent period seems to be the rule, not the exception. Perhaps it’s a strategy to prevent an enemy, such as a specialized seed predator, from growing too common.
I recall, some years back, a one-season burst of a little wildflower called coastal jointweed in my neighborhood. The species was absent, then briefly abundant along roadsides and in vacant lots, and then absent again. But I’m confident that myriad seeds persist in the soil, awaiting some inscrutable set of conditions to launch another generation.
On the less positive side, the process of reproducing by seeds is fraught with failure. It’s helpful to remember that in a stable population, adult individuals only produce enough offspring to replace themselves. If a plant cranks out hundreds or thousands of seeds over its lifetime, only one or two may survive to adulthood. Most of the rest simply die, eaten by something or decaying after winding up in a place that doesn’t offer suitable conditions for either persistence or germination.
But if this circumstance equals inefficiency for the plant, it represents vast bounty from the point of view of the broader ecosystem. Those resources stored in a seed can easily be diverted to serve the needs of other organisms. Most of the Vineyard’s songbird species, for instance, feed primarily on insects during the warmer months — an abundant, protein-rich, energy-laden diet that is especially important for growing nestlings. But in winter, with arthropods much harder to find, the birds that remain here shift largely to a diet of seeds, deploying a wide range of foraging methods to find and devour the surplus product of countless plants.
Seeds are easy to take for granted. And humans, with our fondness for conspicuous color and interesting structure, tend to value flowers more highly than we do the seeds that follow.
But in the plant’s view, the flower is just a means to an end, and it is the seed, the final product, that really matters. The boundless creativity of evolution has worked for tens of millions of years to invent seeds that are rugged, well-provisioned, and capable of moving. And individual plants invest a substantial portion of available resources into seed production.
The result is twofold. The plants themselves persist and, if necessary, even relocate. And the surplus production, all those seeds that don’t successfully germinate, represent a critical source of energy and nutrition for countless other organisms. The natural world, it’s fair to say, runs on seeds.
