As a kid, I always thought that seeds needed to be purchased every year. It was just what we did each spring - looked at the seed catalog and either ordered them or picked them up at the local do-it-yourself store, and while this always seemed to work, it never dawned on me that nature does a pretty good job of doing this for herself.
My marigolds have literally taken over the gardens and though I curse them in the spring when they appear everywhere, I am happy to have them around at this time of year because they are hardy and can stand up to these chilly nights. I used to collect these seeds, but now I just let them seed themselves and then I move them in the spring to the places that I want them.
Lettuce can be a bit more difficult to determine what is the seed, but that is only because we don't allow the lettuce plant to typically live out its entire life cycle - we eat it in its young and tender teenage stage. After it gets too bitter to eat and starts to bolt, it will then form a weird looking flower and then those start to go to seed - save those and you will have lettuce seeds for next year.
There are many horticulturists that will tell you that many of the flowers we buy, or seeds we buy are hybrids and will not produce "true" seeds, and this is entirely true.....the first few years. But, what I have discovered, often through benign neglect, is that flowers and plants, if given half a chance, will revert back to a more natural variety that does produce seeds true to form. I am often reminded of the line in Jurassic Park when Malcolm says to the scientists, "Life finds a way" and he is entirely correct.
So, I meander around the garden and pick a handful or two of seeds off of the flowers, or I cut open the nicest looking tomato and, before throwing it in the pot, I scoop out a few hundred seeds for next year. Some of the plants I simply watch ripen and dry and then shake the seeds out where I want them next year and others I simply let fall and plan on moving them to a new location after they sprout.
A seed is both a plant's last and final hurrah before being annihilated by winter, and it's boundless hope for the future. It will have absolutely no knowledge of whether or not what it produced will ever come to fruition, but it produces them just the same. And I collect them. I am the bridge to the future for many plants - keeping them warm and dry through the cold winter months and them scattering them in the spring to start over. And they, in their turn, take care of me and provide me with a bridge to my future in the form of food.
There have been times, when stuck indoors studying for genetics tests, when I have wondered how Gregor Mendel, the Austrian Monk that established the basics for genetics, could have spent countless days and seasons watching pea plants.....now I understand.