Both of these are bar graphs, and students will need two contrasting color pencils to complete them.  Remind students to add the colors in the color key, and to use the same color scheme for the graphs on both pages.

   Review with students that the chart titles go with the numbers on the vertical axis.  The horizontal axis is labeled with the names of the various food crops.  Be sure they understand, for example, that the number 5 on the first graph represents a crop yield of 5 tons per acre on U.S. farms in 1992.  A ton is 2,000 pounds. 

   It's OK to show students a quick preview of what the finished graphs should look like - make a drawing on the board or project this page on a screen.  But insist that students make their graphs using the data in the table, marking the top of the bars carefully based on the numbers, and then drawing the bars neatly.
  

What the chart shows, page 28

   This graph shows the enormous yield of two important New World crops, corn and the potato, compared to two Old World crops, rice and wheat.  The date, 1992, is 500 years after the first voyage of Columbus.  A ton is 2,000 pounds.

What the chart shows, page 29

   This graph shows the dollar value of the same four crops listed on the previous page.  Remind students that a billion is a thousand million.  Show the figure for corn on the board:  $19,700,000,000. 

   Corn is a very high-yield crop, as the first graph shows.  It is also very nutritious, and can be used in a wide variety of ways.  It can be boiled and eaten right on the cob, or the kernels can be ground into flour for use in breakfast cereal or tortilla shells.  Popcorn is a popular snack, of course.

   Corn is also widely used as animal feed, and even for use in making a kind of alcohol added to gasoline.

   Indians called corn maize, and played a key role in developing the plant into a food crop.  Over the many centuries after they first planted and harvested corn, Indians would have saved seed from plants with the largest largest ears.  As this yearly pattern continued over countless generations, better and better varieties of the plant were grown.

   The process of selection for better varieties has continued on American farms.  For example, corn as it was grown in the 1600s and 1700s was not sweet like the varieties that have been developed since.  Today, the sweet varieties are a regular feature of summer cookouts and picnics.