Columbia subject headings:
Harvard subject headings:
Plants--Effect of cold on--Soviet Union.
Plants--Effect of cold on--United States.
Plants--Effect of drought on--Soviet Union.
Plants--Effect of drought on--United States.
Wheat--Climatic factors--Soviet Union.
Wheat--Climatic factors--United States.
Wheat--Ecology--Soviet Union.
Wheat--Ecology--United States.
Princeton subject headings:
Wheat--Soviet Union--Climatic factors.
Wheat--United States--Climatic factors.