Ionic Relations and Ultrastructure in Ulva Lactuca

Measurements have been made of fluxes of potassium and sodium in U. lactuca. As far as potassium exchange is concerned, the non-free space acts as a single component; the rate of exchange of the 350 ".-equiv/g of potassium is appa.rently limited by )the plasmalemma ,where the flux is aboJlt 100 p.-equiv/g fresh wt./hr. In the dark, the flux drops by about 50%, and can be Mher reduced by inhibitors of o:X:idative phosphorylation.