how to tokenize a paragraph in xslt

**hi i have an xml document as given below** ------------------------------------------------

<catalog>
<book>
Science 
Maths
Physics
Chemistry
</book>

my xslt code is

  <xsl:for-each select="catalog">
<tr>
 <td><xsl:value-of select="book"> </td>
</tr>
</for-each>


----------

the output is

ScienceMathsPhysicsChemistry

But i need it as

Science 
Maths
Physics
Chemistry

Please help me as am new to this