a "huge" table with small rows and culumns

hi,

I have been a postgres user for serveral months. But recently I find a "mysterious" things
in my /usr/local/pgsql/data/base/The_Database_Name/The_table_name.

In a particular table name "fred" there are only 50 rows and 13 columns. The column types are int,
float, varchar, where
varchar's size is restricted to 50. But its size of
/usr/local/pgsql/data/base/The_Database_Name/fred is more than 20M,  and it keeps growing while the
rows number is still 50.

I am using linux (slackware), with postgres as database, Jonas as EJB server, Tomcat and apache
as webserver, the "fred" table is constantly looked up (no updated) by the user.

Thanks in advance for any suggestions.

Cheers

Feng