How can I get a Google Visulization LineChart to display vertical gridlines?

I am usin开发者_StackOverflow社区g javascript to display a Google Visulization LineChart in my web application. How can I get it to display vertical gridlines? I've read about using chg to set them, but as far as I know that only applies when making the chart using the query string method. Could you tell me how to get verticle gridlines when initialising the LineChart as follows:

new google.visualization.LineChart(div.get(0)).draw(data, { title: 'Unique visitors - Previous Month', width: div.width(), height: 330, chartArea: {left:50, width:"90%"}, legend: 'none', yAxis: {title: '(thousands)'} });

You can use a ScatterChart with a positive lineWidth to emulate a line chart. This component supports vertical grid lines through the hAxis.gridlineColor setting.