The mice inside 'erosion'
The source of the word "erosion," or the gnawing effects of water on land, dates back to Roman times. The ancient Romans were pestered by mice and created the term rodere, "to gnaw," from which we get "rodent." Alchemists of the Middle Ages noticed how acid ate through metals and called the biting action of such chemicals "erosion." By 1825, geologists had applied the term to the scarring action of water on land.
When rye, barley, or oats were harvested, a farm worker was likely to be covered with seeds and sweat. A farmhand in such a state was often called seedy, a term later applied to the "rough" clothes he wore and anything rundown or rustic. Gardeners also know if lettuce is not harvested on time, it goes to (form) seed. Similarly, a house or business may go to seed from lack of attention.
SOURCES: 'Loose Cannons and Red Herrings' by Robert Claiborne; 'Why You Say It' by Webb Garrison; 'What's in a Word?' by Webb Garrison; 'The Encyclopedia of Word and Phrase Origins' by Robert Hendrickson.