SUMMARYThree methods have been used to investigate the effects of a number of commercial herbicides on the growth of certain soil fungi: measurements of hyphal extension across agar plates; measurements of hyphal extension along sterilized plant material; and manometric techniques. Three points, in particular, emerged from these studies. First, that there was no stimulation of fungal growth. Herbicide interference in growth included suppression of spore germination, inhibition of the rate of linear extension of the mycelia, and abnormalities in growth habit and in patterns of spore production. Secondly, that some herbicides (e.g. linuron and paraquat) were more fungitoxic than others (e.g. MCPA and simazine) to a range of organisms. Thirdly, that there were differences between fungi in their sensitivity to individual herbicides. All three methods have shown consistent differences between fungi in their ability to tolerate paraquat. Trichoderma viride, in particular, has been found to be sensitive to paraquat. The inhibitory effects were observed at concentrations well within the range likely to be experienced in the field.

The compressibilities of a num ber of organic vapours have been measured at pressures up to 1 atm. and temperatures ranging from 40 to 130° C. The observed second virial coefficients are compared with values calculated from the critical data by the Berthelot equation. The results show two distinct classes of behaviour. Class I is shown by ethane, ethylene, n -hexane, cyclohexane, benzene, diethyl ether, ethyl chloride, chloroform and carbon tetrachloride, where the measured second virial coefficients are in agreement with the calculated values. Class II by acetaldehyde, acetone, acetonitrile, methyl alcohol, where the measured second virial coefficients are consistently very much higher than the calculated values. It is concluded that the vapours of polar substances for which the energy of attraction between molecules, due to dipole interaction or to hydrogen bonding, is larger than kT undergo dim erization. This view is supported by thermal conductivity data. The range of validity of the Berthelot equation for both non-polar and polar vapours is examined.

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SUMMARYExperiments show that the presence of herbicide residues in plant remains may be a potent factor determining the outcome of competition between saprophytic fungi colonizing such substrates. Pairs of fungi were induced to compete with each other for a substrate both in the presence and in the absence of herbicides. In all cases the outcome of competition for a substrate incorporating the herbicide was different from that for the substrate alone. Paraquat sprayed on to potato haulm altered the outcome of competition between Trichoderma viride and Fusarium culmorum in favour of F. culmorum and the same herbicide on wheat chaff suppressed Rhizopus stolonifer in favour of Aspergillus niger. Treatment of leaves of Raphanus raphanistrum with MCPA altered the outcome of competition between Fenicillium notatum and Aspergillus niger in favour of A. niger.

Summary. The effects were determined of paraquat dichloride and Lissapol NX, consutuents of the commercial formulation Gramoxone W, on the rate of oxygen uptake by cultures of Fusarium cutmanmt and Trkkoderma viride. When applied separately, paraquat dichode was less inhibitory than the wetting agent; when applied together, the inhibitory effect was greater than the sum of those obtained separately. Synergism was also observed between paraquat dichloride of commercial purity and a solution containing the additives used m Gramoxone W but without the paraquat dichloride. This effect is thought to be due to increased permeation of paraquat dichioride into fungal mycelia in the presence of a wetting agent. Older cultures were less affected than younger ones by the coniponents of Gramoxone W. The results suggest that the additives used in formulating herbicides may be critical in determining fungitoxicity. Effets des constituants du Gramoxone W sur les taux de respiration de champignons du sol