This excerpt taken from the XEL 10-Q filed Aug 1, 2008.
The holders of shares of Preferred Stock, irrespective of the series thereof, shall be entitled to receive in preference to the Common Stock, when and as declared by the Board of Directors of the Corporation, out of its net earnings or surplus, cumulative dividends at such rate as shall have been fixed for the series of which such shares are a part, and no more, payable to shareholders of record on such dates and for such dividend periods as shall be fixed by the Board of Directors of the Corporation. So long as dividends are in default in whole or in part on a series of Preferred Stock for any prior dividend period for such series of Preferred Stock, any dividends on the Preferred Stock shall be divided among the outstanding series of Preferred Stock for which dividends are accumulated and unpaid for any prior dividend period applicable thereto in proportion to the aggregate amounts that then would be distributable to the holders of Preferred Stock of each such series if all dividends accumulated thereon and unpaid for all prior dividend periods applicable thereto were paid and declared thereon. Dividends on each share of Preferred Stock shall begin to accrue on the first day of the dividend period during which the original issue of a certificate for such share shall occur; provided,
however, that, in the case of any series of Preferred Stock created after May 6, 1970, the Board of Directors, in its discretion, may fix the date of original issue of the shares of such series as the date from which dividends shall accrue.