Polymorphism in Unity with C#

Apple.cs

using UnityEngine;
using System.Collections;

public class Apple : Fruit
{
	public void Start() {
		weight = 0.5f;
	}
}

Fruit.cs

using UnityEngine;
using System.Collections;

public abstract class Fruit : MonoBehaviour
{
	public float weight = 0.2f;

	public float Weight() {
		return weight;
	}
}

Usage.cs

using UnityEngine;
using System.Collections;

/**
 *  Create an empty GameObject in the scene
 *  and attach the Apple component and this Usage
 *  component.
 *
 *  Pressing 'B' will return the proper result
 *  of the Apple component (0.5f), not the 
 *  Fruit base class- despite the retrieval of the
 *  component using `<Fruit>`
 * 
 **/
public class Usage : MonoBehaviour
{
	private Fruit fruit;

	public void Start() {
		fruit = gameObject.GetComponent<Fruit>();
	}

	public void Update() {
		if (Input.GetKeyDown(KeyCode.B)) {
			fruit = gameObject.GetComponent<Fruit>();
			Debug.Log(fruit.Weight());
		}
	}
}