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SUMMARYThe effect in solution culture of iron(II), acetic and butyric acids and ethylene on rooted cuttings of Sitka spruce and Lodgepole pine has been studied and compared with the effects of anoxia. A relative growth rate parameter is employed to reveal changes in the rate of root growth. Possible mechanisms of toxicity and detoxification are suggested and the greater tolerance of Lodgepole pine is discussed in relation to its superior gas transport system. Conclusions are drawn concerning the role played by each of the toxic factors in the field situation.

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The concentration of iron(I1). manganese(I1). ethylene, volatile fatty acids (VFAs) and hydrogen sulphid have been determined in peaty forest soils subject to waterlogging. Although VFAs would merit further investigation, iron(I1) seems to be the only toxin likely to accumulate in sufficiently large quantities to cause root damage.The use of the ion selective electrode for sulphide measurements is criticized.