A user on the java.net forums has reported the need to be able to specify the -Xmn command line argument to unsigned applets. This command line argument is not listed in the documentation for the java command, and appears to be supported only as a compatibility measure for other vendors' JVMs. Its effects can be had by specifying the -XX:NewSize= and -XX:MaxNewSize= HotSpot-specific command-line arguments, which are already in the secure properties list. Having -Xmn also available would be helpful to end users.
See http://forums.java.net/jive/thread.jspa?threadID=34872&tstart=0 .