Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Graph Preparation

"One picture is worth a thousand words."  This familiar expression simply, though eloquently, describes the importance of graphs. Namely, that a graph provides a pictorial and mathematical representation of data that is easy to interpret and can be used to visualize relationships that may have otherwise gone unnoticed. To reap the full benefit of graphical data presentation, a graph must be properly prepared.  Examine any issue of Plant Physiology for examples of good graphs.

At a minimum, a good graph:

• includes a legend. The legend must adequately describe the contents of the graph. It should include, source of plant material (i.e., species), treatments, condition of material, etc. Don't skimp on your legend.  The reader should have a good idea of what the graph is presenting without referring to the text.

• The first graph in a paper is called Figure 1 and the remainder are numbered sequentially.
• labels the axes properly. Include units.
• makes the graph as large as the paper will allow.
• carefully selects the maximum and minimum values for the x and y axes.
• plots, when appropriate, several replicates of a single treatment on the same graph. Use different symbols or colors for each plot.

Most scientific graphs are now prepared by computer and printed on a laser printer. There are many good programs for preparing graphs and they include SigmaPlot, Excel, and Lotus.

A Word About Excel
Many students now use Excel for graphing data.  Although Excel does a decent job, you must be careful when selecting the 'type of graph.'  There will be few, if any, situations in this course for which you will use the "line graph" option.  Line graphs are just another version of a histogram or bar graph.  In our class you will likely NEVER plot a line graph.  Rather, you will want to select XY graph. This is the type of graph used when plotting two variables against one another!  This is a common error.  Use Caution!

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Last updated:  01/07/2009     � Copyright  by SG Saupe