The dark transformations of phytochrome were investigated in two members of the Centrospermae:Mirabilis jalapaL. (Four o'clocks) hypocotyl hooks andSpinacia oleraceaL. (Spinach) hypoeotyls plus cotyledons. After an exposure to red light, decay of total phytochrome was observed in both species. No evidence was found for the dark reversion of Pfr2to Prin sections kept in buffer or when decay was inhibited by sodium azide. The rate of loss of total phytochrome under continuous illumination inMirabilishypocotyl tissue depended on the Pfr/Ptotalratio whether maintained by the red or blue regions of the spectrum. The lack of reversion in the species investigated here, as inAmaranthus caudatusL. (Love‐lies‐bleeding) another member of the Centrospermae, suggests that the order is an exception among dicotyledons and in this respect resembles the monocotyledons.