Mothers are lousy grudge-holders. Do something stupid and they put their hands on their hips and scowl -- for a moment -- then relent, tousling your hair and giving you some big cookie. Buy them a bright-red scarf, and they ooh and aah, never mind that they only wear pastels. This tolerance is the theory on which Earth Day is founded. What began as a hippie-dippy birthday party for Mother Earth evolved awfully easily into the form it took this past week -- a chance for land-despoiling corporations and forest-auctioning politicians to talk about the majesty of nature. Its how Mothers Day might have turned into a major industry, if it hadnt already started out as one. Still, is Mother Earth going to take offense and start carrying on with hourly droughts and famines? No. She doesnt care what you got her; shes just touched that you remembered her birthday.