Bubbles of oxygen from Elodea canadensis were collected and found 5 per mil enriched in 0-18. This confirms the results of both Dole and Vinogradov, who found 0-18 enrichment of photosynthetic oxygen relative to its source, i.e. water. Photosynthesis and respiration appear to have produced the Dole effect, i.e. the 22 per mil 0-18 enrichment of atmospheric oxygen relative to ocean water, its probable source. These results are contrary to findings for both UV photolysis and electrolysis of water both evolving oxygen found depleted in 0-18.