I bought some green bean seeds a week ago, I just ripped open the bag, and there's no way to reseal it. Anyway, a week later I compared the beans I have with the ones still in the store. Mine were a little thinner and edgier (less round around the edges). The two bags are from the exact same supplier. I'm not sure if the shrinkage is from exposure to oxygen or something else.
What accounts for this (pretty small not very noticeable admittedly) change in the beans?
Likely it's mostly related to growing conditions when your seeds were being grown. When conditions near the end of the growing season are optimal (enough water, plenty of sun, ideal fertility) plants tend to make big seeds, packing the extra energy and nutrition into the seeds to help the next generation get off to the best start possible. When conditions are less ideal as the end approaches you get smaller seeds because the plant had less resources to supply the seeds. This isn't to say your seeds aren't good. The seeds you have are fine, the ones at the store just might come up a tiny bit quicker, or have ever so slightly stronger early growth.
I highly doubt it would be an exposure issue, especially in just a week's time. I doubt the package was air tight or fully protected from humidity changes and those are the two major influences I could think of.
