Over time, new seeds replace older seeds, which aren't archived very well,
and over time are lost. When later generations come to the conclusion that
they don't like some of the later optimizations, it is difficult to go back
to the older varieties.
There are many people now who are interested in preserving and exchanging
heirloom seeds. One article I found on the web describes the lengths
people will go to preserve older seeds:
Tending the earth's edible future reached its most poignant
moment--certainly its most courageous--during the Nazis' World War II siege
of Leningrad. The site of the world's largest seed bank--at which Russian
botanist Nikolai Vavilov and his army of ethnobotanists had stockpiled an
astonishing 200,000 species--Leningrad endured 900 days of attack during
which over half a million people starved to death. Surrounded by harvested
seed crops, the collectors martyred themselves rather than consume the
botanical future. And when liberators finally entered the besieged
facility, they found the emaciated bodies of the botanists lying next to
full, untouched sacks of potatoes, corn and wheat--a priceless genetic
legacy for which they paid with their lives.
(Read the full article at:
http://www.metroactive.com/papers/metro/09.05.96/produce-9636.html, which
includes tons of info-tidbits, like the fact that at the turn of the
century there were over 7,000 apple varieties in being grown in this
country.)
It appears there are small heirloom preservation farms across the US -- one
is mentioned in the article above, while another example is the Santa
Barbara Heirloom Nursery, which has a nice web page at:
http://www.silcom.com/heirloom/
You can order limited quantities of seeds from them. Old stalwart Burpee
Seeds also has a beautiful catalog of heirloom seed varieties graced with
reprints of some stunning pcitures of heirloom varieties from their past
catalogs. Available for free off their web page at:
http://www.burpee.com/BPages/heirloom.html
Finally, one of the larger organizations trying to maintain heirloom seed
varieties is the Seed Savers Exchange, at:
http://nj5.injersey.com/~jceres/garden/sse.html
- Jim