[Newbie Question] - Source file from a subdirectory in the Makefile.am

[Danilo Horta]

I have just a directory source tree as follows:

src - +
| - modules

Why i can't include sources from a subdirectory (modules) in the 
src/Makefile.am like that: "hello_SOURCES = hello.c say_bye.c 
modules/calc.c" ?

Automake complains 'automake: src/Makefile.am: not supported: source file 
`modules/calc.c' is in subdirectory'.

$ automake --version
automake (GNU automake) 1.4-p6

Thx