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Seedlings of nine commercial cultivars of oilseed rape were exposed to the field slug Deroceras reticulatum immediately after sowing in compost in trays. There was a small reduction in seedling numbers in the presence of slugs which was not related to glucosinolate concentration in seeds or seedlings. However, the number and leaf-area of seedlings with damage symptoms were strongly and inversely related to the total concentration of glucosinolates in seeds and one wk-old seedlings. The presence of barley seedlings as alternative food did not significantly affect this relationship. The glucosinolate concentration of seeds was closely correlated with that of wk-old seedlings. Analysis of individual glucosinolates in four cultivars spanning the range of concentrations found, showed that the concentration of most components declined as total glucosinolate concentration decreased. However, 2-phenyl ethyl-glucosinolate (gluconasturtiin) concentration tended to increase in seeds and 3-indolyl methyl-glucosinolate (glucobrassicin) increased in seedlings as total glucosinolate concentration decreased. Damage by slugs was inversely related to the concentration of those glucosinolates which decreased and was positively correlated with the two compounds which increased as total glucosinolate concentration decreased. The results support the hypothesis that glucosinolates in brassicas protect them from polyphagous herbivores, and, in particular, that an important function of glucosinolates in rape seeds is to protect seedlings from slugs. As glucosinolate concentrations of oilseed rape cultivars continue to decline, so the risk of slug damage to seedlings may well increase.

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The authors desire to express their appreciation to H. W. ALLINGER, of the Division of Chemistry, who made most of the analyses; also to J. G. SEWELL, of the Division of Chemistry, H. W. SPRAGUE and Miss E. HARROLD, who helped prepare the material for analysis and did a portion of the analytical work. 91

Langmuir and Mackay's data on the rates of evaporation of tungsten, molybdenum and platinum have been corrected to the tungsten temperature scale of Forsythe and Worthing. Similar data on nickel, iron, copper and silver are published for the first time on the same temperature scale. The third law of thermodynamics has been assumed in all calculations and the vapor pressures are calculated from the rates of evaporation. The experimental data check the third law as shown by the constancy of the calculated values of X 0 , the latent heat of evaporation at the absolute zero. Tables are given of the rates of evaporation and the vapor pressures up to the boiling points. The data are compared with those of other investigators. The evaporation of metals heated in an atomic hydrogen flame was very rapid and gave results which confirmed the data on evaporation in vacuum. The values of X D expressed in cal. gm. (atom) -1 and the boiling points in degrees Kelvin are W Mo

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