title: Pandas missing x tick labels
body: <p>When I add <code>c</code> to a pandas plot, x tick labels disappear. Does anyone know how to add them back?</p>
  
  <pre><code>import pandas as pd
  
  df = pd.DataFrame(
      {'mean': {0: 10,
                1: 16,
                2: 18,
                3: 22,
                4: 30},
       'size': {0: 103, 1: 2509, 2: 41939, 3: 145997, 4: 143530},
       'value': {0: 1.5, 1: 4.5, 2: 7.5, 3: 10.5, 4: 13.5}}
  )
  
  ax = df.plot(kind='scatter', x='value', y='mean', s=60, c='size', cmap='RdYlGn') 
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/TGrnS.png" rel="noreferrer"><img src="https://i.stack.imgur.com/TGrnS.png" alt="enter image description here"></a></p>
  
  <p>Tried to manually add x tick labels, but still not working.</p>
  
  <pre><code>ax.set_xticks(df['value'])
  ax.set_xticklabels(df['value'])
  </code></pre>