Change plot title sizes in a facet_wrap multiplot

Question

Can any help me change the title text size for these plots. i.e. make them larger?

Script

ggplot(NMPSCMOR, aes(Length,  fill=Year)) + 
  geom_histogram(position="dodge", binwidth=60,  colour="black") + xlim(0, 600) +
  scale_fill_grey(start = 1, end = 0)+ 


  geom_vline(data=ddply(NMPSCMOR, Year~Morphology~Sector2, numcolwise(mean)), 
             mapping=aes(xintercept=Length,color=Year),  linetype=2, size=1) + 
  scale_color_grey(start=1,end=0)+

  xlab("Length Class") +
  ylab(expression(paste("Total Count"))) + #( ", m^2, ")", sep = 
  facet_wrap( ~ Morphology + Sector2, ncol=3, scales = "free") +
  theme(

    panel.grid.minor = element_blank(),               #removes minor grid lines
  panel.grid.major = element_blank())

Answer 1

In theme(), add strip.text = element_text(size=25) or whatever size you want.