AdSense has a threshold of $100. And as pointed by LISA HW & DABEANER, it gets carried over to next month. And the pay-out happens after almost one month.
At the end of March 2009 (01 March to 31 March) you earn $ 10
April 2009 you earn $ 60
May 2009 $ 35
(at the end of 31 May 2009 = total accumulated earnings are: $105)
By 10 June 2009, this is reflected in your Payment History of your Adsense A/c. Then checks are generated in last week of June 2009. You will receive it in first week of July 2009.