How do I close down apps that show along the bottom of the screen when I double click the home button?

When I double click the home button I can see all the apps which are open along the bottom. I used to be able to make them jiggle and then click on the corner cross of all the ones I wanted to close. I understood that this was recommended to save battery power. I have an iPhone 5 running on IOS7. I've tried to close all the unnecessary apps just now and find that I can't. If I can get them to jiggle there's no cross to close them down. Can anyone give me a solution please?