[R] How to change the font size on the title of a xyplot

[Eduardo M. A. M. Mendes]

Hello

I am using xyplot (lattice) to plot a xts variable.  There are 20 variables within the xts variable (index by a datetime vector sampled every 1 minute).  The results are very nice and help me to understand what is going on with the data. However since the names (labels of each variable) within the xts variable are large, the title of each plot is cropped.   How can I select the font size of the titles without changing all other fonts?

Many thanks

Ed