Greek Prime Minister George Papandreou’s surprise announcement that Greece will vote on its planned bailout has sent world markets into a tailspin. Analysts worry the  planned referendum will undermine the agreement reached at meeting of European leaders in Brussels last week and bring Greece dangerously close to defaulting on its debt. In the U.S., brokerage firm MF Global filed for bankruptcy on Monday, in part due to bad bets made on European debt. Traders, however, say worries about the euro zone are primarily responsible for the volatility. Louise Story, Wall Street and finance reporter for The New York Times, reports on the latest.