[AccessD] Hitting Upper Limit of 401 Characters in String Building

I'm building big strings to populate what look like spreadsheet cells on a
report.  I wasn't sure how much data the client would be entering in the
text fields that go into the strings, but I expected to run into a 255 or
256 chr limit.  Apparently, the limit I'm hitting is 401.  Do anyone know,
off hand, why 401 is a magic number?  My last recourse, I guess, is a temp
table with a memo field.  I know I can open a recordset on a memo field and
append to it build up long strings.