Lamb's quarter is a common weed that interferes with the growh of corn.  
An agricultural researcher planted corn at the same rate in 16 small plots
of ground, then weeded the plots by hand to alow a fixed number of lamb's
quarter plantes to grow in each meter of corn row.  No other weeds were allowed
to grow.  The datasets has two variables measured on each plot.

          weeds per meter
          corn yield (in bushels per acre)