How to do it...

1. Add the following member variable to the odor-particle script to store its parent ID:

public int parent; 

2. Create the new odor-enabled class, deriving from the original vertex:

using UnityEngine; 
using System.Collections; 
using System.Collections.Generic; 
 
public class VertexOdour : Vertex 
{ 
    private Dictionary<int, OdourParticle> odourDic; 
} 

3. Initialize the odor dictionary in the proper function:

public void Start() 
{ 
    odourDic = new Dictionary<int, OdourParticle>(); 
} 

4. Add the odor to the vertex's dictionary:

public void OnCollisionEnter(Collision coll) 
{ 
    OdourOdourParticle op; 
    op = coll.gameObject.GetComponent<OdourParticle>(); 
    if (op == null) 
        return; 
    int id = op.parent; 
    odourDic.Add(id, op); 
} 

5. Remove the odor from the vertex's dictionary:

public void OnCollisionExit(Collision coll) 
{ 
    OdourParticle op; 
    op = coll.gameObject.GetComponent<OdourParticle>(); 
    if (op == null) 
        return; 
    int id = op.parent; 
    odourDic.Remove(id); 
}

6. Implement the function for checking whether any odor is tagged:

public bool HasOdour() 
{ 
    if (odourDic.Values.Count == 0) 
        return false; 
    return true; 
} 

7. Implement the function for checking whether a given type of odor is indexed in the vertex:

public bool OdourExists(int id) 
{ 
    return odourDic.ContainsKey(id); 
}