The Board of Regents shall have exclusive authority to confer degrees and grant diplomas, but each college may, in its discretion, grant rewards of merit to its own students. No student upon graduation shall receive any diploma or degree unless he shall have been recommended for such honor by the faculty of the college in which he shall have pursued his studies. The board shall also have power to confer the usual honorary degrees upon other persons in recognition of their learning or devotion to literature, science, or art; but no degree shall be conferred in consideration of the payment of money or other valuable thing.