why '&' changes the behaviour of the object?

Question

I'm studying C++ form Thinking in C++ V1. I came across an example that demonstrates inheritance. Here it goes

#include <iostream>

class Instrument{
public:
    virtual void play(){
        std::cout<<"instrument::play()";
    }
};

class Wind: public Instrument{
public:
    void play(){
        std::cout<<"Wind::play()";
    }
};

void tune(Instrument& i){
    i.play();
}
int _tmain(int argc, _TCHAR* argv[])
{
    Wind flute;
    tune(flute);
    return 0;
}

This outputs Wind::play() on the console.

But if I change the method 'tune' to

void tune(Instrument i){
    i.play();
}

The output will instrument::play()

Since the '&' is added so that the reference of flute is passed instead of a copy, why does the program output instrument::play() instead of Wind::play() ?

Answer 1

Because the copy that gets passed has type Instrument, not type Wind, because Instrument is the type that the function takes. This is known as "slicing".