[xsl] separate white space and show in combo individually

Perl code

<CODE>
$str=$in{'values_separated_by_space'};
my $results = $stylesheet->transform($source, arg  => "'$str'",val => "'1'");
</CODE>

"$arg" contains any number of space separated values say "abcd pqrwr
xyz dd3 24322" and I want these values in a combo box individually
using xsl file.What should I do?

I only know this much code..:(

<xsl:for-each select=(till values are there)>
 <select>
     <option>
           <xsl:value-of select="substring-before($arg,
' ')"/>
     </option>
 </select>
</xsl:for-each>