Photosynthetic rates of Typha latifolia, the broad-leaved cattail, are the equivalent of rates reported in tropical grasses and other plants which assimilate carbon by the phosphopyruvate carboxylase reaction, but photosynthesis in T. latifolia proceeds by a typical Calvin cycle. Glycolate oxidase, the photorespiratory enzyme, is present in high concentration in this species, but only minor quantities of the assimilated carbon pass through the photorespiratory pathway. However, continued operation of the pathway is apparently essential in the maintenance of assimlilatory capacity. Glycolate oxidase function is not closely coupled to stomnatal operation in T. latifolia.
Among the most efficient dry matter producers known are cattails, members of the aquatic genus, Typha (30). A brief report of the effect of oxygen upon the assimilatory efficiency of Typha angustifolia (12) suggests that this high efficiency may be associated with the ribulose-1, 5-diP pathway. Studies of glycolate oxidase level have also demonstrated a high photo- respiratory capability in Typha latifolia (21). The experiments reported here were designed to: (a) determine photosynthetic rates of Typha directly by infrared gas analysis, (b) establish the nature of the carboxylation reaction, and (c) estimate the pro- portion of the carbon assimilated which passes through the glycolate oxidase reaction.