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Summary Intact Myriophyllum spicatum plants were grown in compartmentalized containers in a growth room so that the roots were separated from the shoots by a watertight partition. Nitrogen 15N was added to the water or sediment to trace the uptake of inorganic N by the plant shoots or roots. Myriophyllum spicatum is capable of taking up inorganic N through both roots and shoots. Plant N requirements can apparently be met by root uptake alone. However, when about 0·1 mg/l of NH4‐N were present in the water, foliar uptake supplied more N to the plants than did root uptake. Foliar uptake of NH4‐N was found to be several times faster than that of NO3‐N when both forms of N were present in the water. Only about 1% of the N taken up by the roots was subsequently released to the water through the foliage.

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T o evaluate the net N and P contribution to water from herbicide-killed aquatic weeds, water milfoil containing 1.5% N and 0.30% P was killed with endothal and allowed to decompose, in the dark, in water only or sedimentwater systems. Changes with time in dry weight, total N and P, and organic C in the plant material, and organic and inorganic forms of N and P in the water were determined. Plant decompostion was limited by N. Inorganic N was released by the sediment, and decomposition was more rapid when sediment was present. A smaller N requirement for decomposition under conditions of low 0, was postulated as a possible explanation of the more rapid decomposition observed in the absence of aeration. The presence of plant P in excess of decomposition requirements resulted in rapid accumulation of organic P, followed by inorganic P, in the water. Organic N appeared in the water early in the experiments, but was depleted rapidly, and inorganic N was apparently immobilized as soon as it was formed. I n the presence of sediment, organic N and inorganic P levels were much lower. On treating of water milfoil with herbicide, rapid P release can be expected. This P can either be utilized in further biomass production or be sorbed by the sediment. Insufficient data were available to reach definite conclusions regarding N. It would appear, however, that N release from decaying weeds is much slower than P.Higher plants play an important role in aquatic ecosystems. They provide food and oxygen for other organisms, as well as serving as places of attachment and shelter, and as spawning areas for some fish. But in many fertile water bodies aquatic weeds are a decided detriment to man's use of these waters. Rooted in shallow areas of lakes and ponds, aquatic macrophytes increase in abundance as they

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