There shall be a rebuttable presumption that all property, real and personal, acquired by the husband or the wife, or both, after marriage, or on or after the effective date of this act, whichever is later, is community property: Provided, however, That nothing contained in this act shall prevent a husband and wife from acquiring and holding property in any manner permitted by law prior to the effective date of this act. Such presumption shall be deemed to be rebutted in any instrument of conveyance of real property where the grantees therein are described as husband and wife.