He meant that the Memorial Plaza is so weighted with meaning, and emotions run so deep, that something as common as a dying tree could take on symbolic significance.

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Dr Packer and Dr Clay studied the black cherry, a tree that is common in Indiana and other areas of eastern North America.

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If you want to understand what is happening there, imagine: Under the Liberty Tree that stood in Boston Common, early in the first American Revolution, any and all could come to air their grievances and hammer out solutions collectively, and it was there the promise of American democracy first took root.

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Common causes include foods such as peanuts, tree nuts, sesame, fish, shellfish, dairy products and eggs.

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According to Allergy UK, peanut and tree nut allergy is the most common food allergy in adults and children.

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Some common allergy triggers are milk, shellfish, legumes, sesame, eggs and tree nuts like almonds and walnuts.

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But if those advocating a euro breakup are barking up the wrong tree, so too are those arguing for the immediate creation of common euro-zone bonds and a banking union.

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Since 2006, food manufacturers have been required to clearly label products that contain any of the most common allergens -- milk, eggs, fish, shellfish, peanuts, tree nuts, wheat and soy -- but some allergy experts say the labels should be more explicit.

CNN: The story