THE BASIS OF THE DIFFERENTIAL PHYTOTOXICITY OF 4-HYDROXY-3,5-DI-IODOBENZONITRlLE*

Summary. Entry of ioxynil-¹⁴C into portions of leaves was greater with mustard than with barley or pea and was unrelated to stomatal density. Measurement of ioxynil content of sprayed plants showed that by increasing the concentration of ioxynil and adding a surfactant, almost as much ioxynil could be made to enter barley as entered mustard from a lower concentration without surfactant. Auto radiographs showed that a limited amount of ¹⁴C was translocated to a small extent in plants following localized application of ioxynil-¹⁴C. An experiment comparing leaf removal by cutting with destruction of equivalent leaf areas by ioxynil treatment suggested a greater translocated effect of ioxynil with mustard than with pea or barley. Les principes de la phytotoxicité différentielle du 4-hydroxy-3,5-di-iodobetZonitrile II. Absorption et migration     

EFFECT OF PARAQUAT ON MICROBIAL ACTIVITIES IN SOILS*

Summary. When paraquat was added to four different soils, nitrification was not appreciably affected but ammonification of soil organic-matter nitrogen was slightly retarded. Carbon dioxide evolution as well as oxygen consumption was used as an index of metabolic activity of soil micro-organisms and paraquat had a stimulatory effect at higher concentrations. Oxidation of added sulphur was slightly depressed. Paraquat decreased both the total mould and bacterial populations in Chehalis silt loam. After 30 days incubation the percentages of Streptomyces and Penicillia were markedly increased by most treatments but were little affected in Chehalis silt clay and Woodburn soils. Except for the temporary suppression of nitrification, paraquat had no significant influence on general microbial activities of importance to soil fertility. Some bimodal effects or toxicity inversions were observed with intermediate concentrations. Effet du paraquat sur les activités microbiennes dans les sols     

THE YIELD AND QUAEITY OF RED BEET SEED AS AFFECTED BY DESICCANT SPRAYS AND HARVEST DATE

Summary. Diquat and sodium monochloroacetate (SMA) were used to desiccate seed crops of red beet in experiments from 1963 to 1965. The seed plants became brown and dry about 7 days after spraying and were then judged suitable for combine harvesting, although this was not done in these experiments. Yields of seed 7 days after spraying were as good as those from the control plants, but were lower than the control yields when harvested 14 days after spraying. In laboratory tests in moist sand at 20° C the percentage of the embryos which germinated was not markedly affected by diquat or SMA treatment. The emergence of seedlings in the field, however, was affected adversely by treatment of the seed crop with 11 and 22 oz/ac of diquat ion in 1963 and by SMA at 20 lb/ac in 1964 and 1965. Diquat at 6·6 oz/ac in 120 gal/ac water in 1964 and 1965 had no serious adverse effects on embryo emergence. Residues of diquat ion in seed varied from 2 to 4 ppm, but the impairment of embryo emergence by diquat was believed to be due to the premature arrest of growth of the seed on the desiccated plants.
It is concluded that when harvesting conditions are poor, desiccants could be valuable.
Influence des traitements dessicants et de la date de récolte sur le rendement et la qualité de la sentence de betterave rouge     

THE COMBINED ACTION OF 3-AMINO-1,2,4-TRIAZOLE AND AMMONIUM THIOCYANATE ON PHOSPHATASE ACTIVITY IN COTTON THISTLE (ONOPORDUM ACANTHIUM L.)

Summary. In phosphatase extracts prepared from untreated leaves of Onopordum acanthium , phosphatase activity was stimulated by amitrole (0·04 M) and ammonium thioeyanate (0·04 M), alone and together. The effect of the mixture of amitrole and ammonium thioeyanate was more than additive in experiments set up at pH 4·0, less than additive at pH 4·6 and roughly additive at pH 5·3 and 5·8. The effect of amitrole alone could be explained simply in terms of the increase in pH it effected.
In leaves harvested 4, 7 and 9 days after spraying rosettes with 1/8 lb/ac (140 g/ha) amitrole and 1/4 lb/ac (280 g/ha) ammonium thioeyanate, alone and together, more than additive or additive increases in phosphatase activity of plants sprayed with the mixture were recorded. These increases are interpreted as being due to increases in the amount of soluble protein.
Inorganic phosphate levels showed different trends with time in plants treated with amitrole alone compared with plants treated with the mixture of amitrole and ammonium thioeyanate.
These interactions between amitrole and ammonium thioeyanate are taken to indicate a possible chemical basis for the increased herbicidal activity of the mixture over amitrole alone.
Histochemical studies on the mature leaves of rosettes showed that phosphatase activity was confined to the vascular tissues while in the very young leaves it was high in the chlorenchymatous tissue and appreciable in the epidermal and hair cells.
Attention is drawn to the strong buffering action of amitrole in the pH range 4·0–5·3. This may be relevant to herbicidal activity, the vacuolar pH of the outer cells of leaves of Onopordum being in the range 4·8-5·2.
L'action combinée du 3-amino-1,2,4-triazole et du thioeyanate d'ammonium sur l'activité de la phosphatase chez Onopordum acanthium L.