Proof of citizenship, under sections 21, 22 to 24, 26 to 28, 29, 30, 33 to 48, 50 to 52, 71 to 76 of this title and , may consist, in the case of an individual, of his own affidavit thereof; in the case of an association of persons unincorporated, of the affidavit of their authorized agent, made on his own knowledge, or upon information and belief; and in the case of a corporation organized under the laws of the United States, or of any State or Territory thereof, by the filing of a certified copy of their charter or certificate of incorporation.section 661 of title 43