template implementation... bad syntax?

hi again
here is a trouble that I used to skip... now that came the time to solve it, I couldn't find the solution:

avl_tree.h

Code:

#ifndef AVL_TREE_H
#define AVL_TREE_H

template <class T>
class avl {
	public:
		avl ();
		~avl ();
};

#ENDIF

avl_tree.cpp

Code:

#include "avl_tree.h"

template <class T> avl<T>::avl() {}

template <class T> avl<T>::~avl() {}

My "main.cpp" program will #include "avl_tree.h".
If I compile "main.cpp" and "avl.cpp" and link them together, it's all ok.
But if I main.cpp contains an instantiation

Code:

avl<int> tree;

I get from the linker:
g++ -O0 -g3 -o test main.o avl_tree.o
main.o: In function `__tcf_1':/home/.../src/main.cpp:11: undefined reference to `avl<int>::~avl()'
main.o: In function `__static_initialization_and_destruction_0':/home/...main.cpp:11: undefined reference to `avl<int>::

what am i missing?

Read the answer to: Why can't I separate the definition of my templates class from it's declaration and put it inside a .cpp file?

thanks laserlight
I should have read that page better when you already posted it before
After reading I wanted to know how the STL has been implemented:
Is the whole code into headers, or do they use other solutions? Those weird headers have made me a bit confused.

>> Is the whole code into headers
The ones I have looked through have their template code implemented entirely in headers.