Concern over the Ukrainian situation is given as the reason for today's U.S. stock market plunge. Grain and soy markets chopped around on both sides of yesterday's closes in nervous fashion. General Comments With Crimea's referendum over secession from Ukraine and potentially joining Russia scheduled for this weekend, the rhetorical barrage from the EU, U.S. and Russia is escalating. The West is pressing Russia to negotiate and threatening massive sanctions if it does not, but President Putin describes the situation as a domestic Ukrainian affair for which his country is not responsible. He shows no sign of acceding to the West's demands, and no one can predict with confidence how this standoff will end. Until equity and derivative marke...