Catenating strings involving plotmath symbols.

In the context in which I am actually working it is necessary for
me to build parts of a text string to place on a plot in two separate
stages.

The following toy example illustrates what I am trying to do:

L1 <- substitute(list(paste("Bias in ", gamma,", ")))
L2 <- substitute(list(beta==b0),list(b0=300))

plot(1:10,main=L1) # Works fine.
plot(1:10,main=L2) # Works fine.

But what I want is the catenation of the strings contained in L1 and L2.
I thought that I might just be able to catenate them using c(), as in

plot(1:10,main=c(L1,L2))

but this just gives me the "L1" title, and L2 gets ignored.

Is there any way to accomplish my goal?

(Please don't tell me how to build a single string to use as a title;
I know how to do that. ?I need to be able to build two separate
strings and then combine them somehow.)

It seems to me that it should be do-able, but I have no idea where
or how to look for the appropriate incantation. ?Googling around,
I found lots of stuff on how to catenate vectors or paste together
"ordinary" text strings, but nothing on how to catenate mathematical
expressions.

Can anyone help me out?

? ?cheers,

? ? ? ?Rolf Turner