I tipped my hat to Earth Day by hearing Kent Whealy, the visionary behind The Seed Savers Exchange, speak to a group of gardening die-hards Friday night. It would be impossible to hear him speak and then be able to look at a vegetable in quite the same way ever again.

Whealy and his wife founded the network of heirloom seed traders 20 years ago and also oversee Heritage Farm, a 890-acre operation near Decorah, Iowa, where they harvest seed to keep some 25,000 varieties viable for the long haul. Each year the Heritage farm staff plants 10 percent of the inventory on a 10-year rotation. Seed is dried and stored in a climate-controlled facility where it has a shelf life of 40 to 50 years.

The exchange disseminates seed through a catalog and Web site (www.seedsavers.com) and facilitates a network of 800 seed savers who make their seed available to others.

The mission, simply put, is to preserve the diversity in food that existed naturally but has become depleted by modern lifestyles. By reintroducing disappearing seed into the food chain, Whealy hopes to reverse this process. One factoid Whealey offered tells the story. At the beginning of the 20th century, there were more than 7,000 named apple varieties; now he can locate just 700.

At that time, people were more likely to be growing their own fruit and vegetables from seeds that had been passed down to them for generations, in many cases predating their forebears’ migration from other parts of the globe. In this way, people kept heritage strains alive and preserved a greater variety of food than we have now.

In other words, this was a time when Blue Lake and Kentucky Wonder didn’t define the green bean.

Ponder that. As generations of nongardeners have given up the family seed and mass production has streamlined our food choices, we actually have lost a good deal of variety. Now when we think tomato, we think red and round. Gone from our mental inventory are the yellow, pink, purple, green, striped and speckled fruits in assorted shapes and sizes that once were recognized as tomatoes.

We acknowledge this standardization of the American diet in franchised fast food, but we are not accustomed to thinking of produce as a victim of this same phenomenon. While Whealey didn’t frame it this way, what he’s really doing is battling McVegetable.

Whealy’s weapon is the slide show, which displays image after image of the rainbow of long-forgotten fruits and vegetables. He hopes that seeing is believing.

“It’s difficult to make people see genetic erosion as a threat,” he said. “It really takes showing them the variety, showing them the beauty to really touch their hearts.”

The volume of what Whealy has preserved seems staggering, although it represents just a fraction of the fruits and vegetables that human beings have eaten over time. The Heritage Farm seed collection includes 5,000 varieties of tomatoes, 2,000 peppers, 1,200 peas, 1,500 lettuce, 650 potatoes and 300 garlic.

The key is for people to grow the uncommon vegetable.

“We have to instill this love of gardening in our children, because if we don’t, we won’t have anyone to pass this material on to,” Whealy said. “Just so much of it could be lost right now. This is all the genetic material we’ll ever have available, right here.”