[R] How to show the intermediate tick marks without the values in a different color

[xpRt.wannabe]

Is there a way to show also the intermediate tick marks without the
values?

Example:

plot(cars)

What would one do to show the tick marks in, say, gray color at the
increment of 1 without showing the actual values in-between the default
x
values: 5, 10, 15, 20, 25?

platform i386-pc-mingw32
arch     i386
os       mingw32
system   i386, mingw32
status
major    2
minor    2.1
year     2005
month    12
day      20
svn rev  36812
language R

Thanks,