error CS1061: Type `UnityEngine.ParticleSystem' does not contain a definition for `emission' and no extension method `emission' of type `UnityEngine.ParticleSystem' could be found (are you missing a using directive or an assembly reference?)

using System;
using UnityEngine;

namespace UnityStandardAssets.Effects
{
    public class ExtinguishableParticleSystem : MonoBehaviour
    {
        public float multiplier = 1;

        private ParticleSystem[] m_Systems;


        private void Start()
        {
            m_Systems = GetComponentsInChildren<ParticleSystem>();
        }


        public void Extinguish()
        {
            foreach (var system in m_Systems)
            {
                var emission = system.emission;
                emission.enabled = false;
            }
        }
    }
}

Help!
How to fix it?