tmpar <- par( mar = c(3.1,2.1,.1,.5), mfrow = c(1,2) )

hist( cloning$titer, xlab = "" )
mtext( "(a) raw data", 1, 2 )

hist( cloning$titer - predict(cloning.fit), breaks = seq( -700, 800, by = 100 ),
   xlab = "" )
mtext( "(b) residuals", 1, 2 )

par( tmpar )