XPath Question (related to Java)

Hi, I have the following xml which gets read from a file as part of a Node:
           <Definition> An organic compound in which the aldehyde
group (HC=O) is connected to a branched or unbranched open chain of
carbon atoms rather than a ring. Some aldehydes are created during the
reactions of oxidants used as disinfectants, particularly ozone
(O<sub>3</sub>), with natural organic matter. </Definition>

When I run it through the following method  it ignores the <sub></sub>:
     public String getDefinitionFromNode(Node node) throws
javax.xml.xpath.XPathExpressionException
     {
           XPath xpath = XPathFactory.newInstance().newXPath();
           String definitionExpression = "Definition";
           String definition = (String)
xpath.evaluate(definitionExpression, node, XPathConstants.STRING);
           if(definition.contains("<"))
                 System.out.println ("found a <");
           else
           {
                 System.out.println ("did not find a <");
           }
           return definition;
     }

did not find a <
--------------------------------
<dictionary n=""><TermName>aliphatic aldehyde</TermName><Definition>An
organic compound in which the aldehyde group (HC=O) is connected to a
branched or unbranched open chain of carbon atoms rather than a ring.
Some aldehydes are created during the reactions of oxidants used as
disinfectants, particularly ozone (O3), with natural organic
matter.</Definition></dictionary>

The complete node is:
       <Term>
           <Entry> aliphatic aldehyde </Entry>
           <Definition> An organic compound in which the aldehyde
group (HC=O) is connected to a
               branched or unbranched open chain of carbon atoms
rather than a ring. Some aldehydes
               are created during the reactions of oxidants used as
disinfectants, particularly
               ozone (O<sub>3</sub>), with natural organic matter.
</Definition>
           <SeeAlso>disinfection by-product</SeeAlso>
           <IMAGE fileName="A-17.gif"/>
       </Term>