no further. The growisofs commands I used were simply
         growisofs -Z  /dev/sr1 dirtree1
         growisofs -M /dev/sr1 dirtree2
Only Session1 (dirtree1) is visible under Linux, but both sessions can 
be seen
using the Wibdows utility (CDRoller). How do I include a toc in Session2? Thanks, Roger Young.