Summary The activity of GR7 and Striga germination stimulant(s) from Euphorbia aegyptiaca Boiss. showed adequate persistence (6–8 days) in acidic soils (pH 5·0–6·3), but residual activity was short (1–3 days) in alkaline soils. The compounds tended to lose activity at a faster rate in the alkaline clay Gezira soil (pH 7·8), than in its sandy equivalent (pH 8·1). In solution, pH had no influence on initial activity, but residual action was reduced more rapidly by alkalinity and high temperature. However, the rate of loss of activity in solution was slower than in soils.

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Summary Aqueous extracts of fifteen Euphorbia species induced germination of Striga hermonthica (Del.) Benth. seeds to varying extents. Extracts from E. supina Raf., E. pilulifera Jacq., E. acalyphoides Hochst. ex. Boiss, E. prunifolia (Jacq.) Hort. Schoent., E. hirta L., E. aegyptiaca Boiss, E. splendens Boj., and E. granulata Forsk, were the most active. Extracts from E. acalyphoides and E. pilulifera were inhibitory at high concentrations. Undiluted extracts from E. pilulifera, E. aegyptiaca and E. hirta induced haustorial initiation. The stimulatory substance(s) were widely distributed in plants of E. aegyptiaca. Extracts from E. aegyptiaca also stimulated seed germination and haustorial initiation in a range of Striga species and strains.

The composition of the oils from three varieties of New Zealand‐grown linseed have been determined and compared with that of a sample of Indian linseed oil. Some observations on the separation of the component fatty acids are reported.

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The separation of linseed oil fatty acids by counter‐current distribution between pairs of solvents has been investigated and a linolenic acid concentrate, containing linoleic acid only as impurity, has been obtained.

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