The anilides and para-chloroanilides have been prepared from the first four homologues of the 3-and 5-alkylsalicylic acid series and the fungistatic activity of these compounds has been assessed by two methods. In tests against mycelium, the chloroanilides usually induced less retardation of growth than the corresponding anilides. The effect of introducing an alkyl grouping was in general to reduce the fungistatic effect but with the n-propyl derivatives this trend was less marked. Salicylanilide gave the greatest over-all inhibition of the fungi investigated.

Light-induced inhibition of the elongation of primary roots of Zea mays seedlings is dependent upon the perception of light by the root cap. Separate exposure of detached root caps and roots from which root caps have been removed (i.e. decapped roots) to white light or darkness has shown that the elongation of a dark-exposed root to which a light-exposed root cap is attached is inhibited significantly, whilst a light-exposed decapped root to which a dark-exposed root cap is attached is not inhibited. Thus the decapped root is not capable of perceiving the growth-inhibitory stimulus of white light and its rate of elongation is greater than that of light-exposed roots with root caps still intact. However, the capacity to perceive light and, therefore, to be inhibited by it, is restored to the decapped root approximately 5 h after removal of the root cap.Abscisic acid and two unidentified growth-inhibiting compounds are present in the root caps of light-grown but not of dark-grown Zea mays seedlings and a period of 2.5-3.0 h is required for transport of the compounds, in levels effective in growth inhibition, from the root cap into the apex of the root.

No abstract

The toxicity of potassium iodide towards bean plants (Pha,^eolus vulgaris) is greater in the light than in the dark. Treatment of leaf discs in ihe dark or the light reduces photosynthetic activity to the same extent, but the loss of chlorophyll is less pronounced in the dark. Iodine behaves similarly but is cfTcctive at lower concentrations. Iodide does not inhibit chlorophyll synthesis. IcxJine is some 10' tim« as effective as iodide in inhibition of the Hill reaction in isolated chloroplasts. 'lTicsc results are consistent with the hypothesis that icKiidc toxicity is a result of intraccllular oxidation to iodine. Action herbicide de I'iodwe de potassium. Effet sur la teneur en chlorophylU et la photosynthise sur le haricot nain (Phaseolm vulgaris)R^sum^. La toxicil^ de I'iodure de potassium vis-i-vis du haricot {Phaseoltis Dulgaris) i-st plu.i grande i la lumiere qu'A I'obscuriti^. Le trailemcnl de portions de feuilles k I'obsrurit^ ou h la lumiere riduit I'activitt photosynth^tique dans la meme proportion mais la perte de chlorophylle est moins martjut^e k I'obscurit^. L'iodure de potassium agit de fa^on analogue mais il est actif 4 des concentrations plus faibles. II n'inhibe pas la synthese de la chlorophylle, L'iode est environ 10* fois plus aclif que l'iodure dc potassium en ce qui conceme I'inhibilion de la reaction de Hill sur des chloroplastes isol^a. Crs r^iultats concordent avec Thypothese que la toxicitt^ de l'iodure dc potassium est le rt^suttat d'une oxydation intraecllulairc en iode, Herbizide Wirkung von Jodid. Wirkung auf Chlorophyllgehalt und PhotosynUuie bei der Buxhbo/me (Phaseolus vulgaris) Zusammenfassung. Die Toxi2itat von Kaliumjodid auf Bohnenpfianzen {Phaseolus vulgaris) ist im Licht starker als im Dunkein, Die Behandlung von BiiiUscheiben im Licht oder im Dunkein vermindert die Photosynthese gleichrrmassen, aber im Dunkein ist der Verlust an Chlorophyll weniger ausgepragt. Jod hat ahnlirhe Eigenst haftcn, aber ist bei niedrigerrn Konzentraiionen wirksam. Die Hemmung der Hill-Keaktion in bolierten Chloroplasten ist durch Jod etwa 10^ mal wirksamer als durch Jodid, Diese Ergebnisse stimmen mit der Hypoihese uberein, dass die Toxizitat von Joaid auf die intrazcllularc Oxidation von Jod zuKiekzufuhren ist.

Investigations into the relationship between the light-induced inhibition of root elongation and the response of Zea mays primary roots to gravity have revealed a close similarity between growth-inhibiting factor(s) produced in response to both stimuli. Evidence is presented that the inhibiting factor(s) produced in the root cap on exposure to white light can be used by the root to produce curvature in response to gravitational stimulation in darkness, i.e. under conditions in which dark exposed roots do not normally respond to gravity.The implications of these findings on the way in which roots respond to geotropic stimulation are discussed.

SUMMARYThe inactivation of the herbicide ioxynil by contact with soil has been investigated. Shaking solutions of the sodium salt with acid soils led to a precipitation of the herbicide. With alkaline soils, a small amount of ioxynil became adsorbed on the soil particles. With unsterilized soils, hydrolysis to 3,5‐diiodo‐4‐hydroxybenzoic acid occurred, with 3,5‐diiodo‐4‐hydroxy‐benzamide as an intermediate product. Liberation of iodide ion in this system was also demonstrated.The phytotoxicity of ioxynil is enhanced by exposure of treated plants to light. The reduction in chlorophyll level of bean leaf tissue treated with ioxynil and other dihalogenohydroxybenzonitriles when exposed to light has been determined. Evidence is presented showing that although ioxynil is poorly translocated in the dwarf bean plant, its degradation products appear in the shoots of these plants after the herbicide has been supplied through the roots.

No abstract

3,5-Diiodo-4-hydroxybenzoic acid (DIHB) has been shown to exert an inhibitory effect on the formation of ethylene by the roots of intact cress Lepidium sativum seedlings in light, and by excised cress root segments. Adding IAA to the culture solution greatly promoted ethylene production, which was suppressed by DIHB. The findings together with results obtained with dinitrophenol (DNP), L-methionine and L-ethionine and also the horseradish peroxidase/methional system of Yang are discussed.The results indicate that the effect of DIHB in promoting the root growth of cress seedlings in nutrient solution in the light operates, at least in part, by suppressing the formation of the root growth inhibitor ethylene.