why copy constructor is not being called?

Hi

Could you please tell why copy constructor is not called in the first
line in main(), as mentioned in the text books. I used g++ version
4.1.2 on debian etch

thanks
suresh

# include <iostream>
using namespace std;
class base
{
  char s;
public:
  base( ){cout<< "construction" << endl;}
  base(const char a ) {cout << "construction with arg" << endl;}
  base(const base & a){cout <<"copy constructor" << endl;}
  base & operator=(const base & a){cout << "assignment operator" <<
endl;}
  ~base( ) {cout << "destruction" << endl;}
};

main ( )
{
  base b1 = 'x'; //why copy constructor is NOT called here as given in
books?
  base b2 = b1; //copy constructor is called

}