On the stiellähme of the grape vine. II. Investigations on the causes of the disease Summary.-In order to analyse the metabolic cause of the "Stiellähme", growth hormones were applied to both healthy and diseased rhachis, the content of native auxin in the berry was investigated and, using histological preparations, the ca ++ distribution in the peduncle tissues was determined. 1. The localized application to the rhachis of the growth hormones ß-indole acetic acid (IAA) and gibberellic acid

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... , both separately and combined, brought about a stronger formation of the collenchyma cell walls of the cortex and an activation of the cambium. GA caused the development ·of numerouf, non-lignified xylem cells, while applications of GA + IAA gave rise to robustly walled parenchyma cells, sclerenchyma cells and lignified metaxylem. The application of growth hormones reduced the occur­ rance of diseased grapes from 25 ° /o to 6-10 ° /o. 2. An early spraying of a-naphthalene acetic acid reduced the amount of grapes with secondary symptoms, however, it did not reduce those with primary symptoms. Later sprayings were unsuccessful. Sprayings of GA or CaC1 2 ' even when combined, did not bring about a decrease in the disease. 3. The investigations concerning the auxin content of grape berries (1968) of the cultivars Riesling and Kerner showed a slow increase in auxin content during the first 3-4 weeks after the berry pollination (Phases I and II of berry growth), followed by a rapid increase within approximately 20-30 days and a maximum of 8-24 µg IAA­ equivalents/g dry weight. In biological tests carried out a few days after the maximum had been attained, no auxin was found to be present. 4. The incinerated cuttings of diseased peduncles showed a comparatively higher ash content in the collapsed zones than in the neighbouring healthy cells. Colouring with alizarine red and titan yellow + NaOH showed increased contents of Ca and Mg. 5. The results are discussed and interpreted in the light of the physiological changes during phase III of berry growth. lt is assumed that the relative lack of ca ++ started the disease and was occasioned by the fixing by organic acids of the Ca-'+ and the decrease in the subsequent ca ++ delivery to the rhachis. Einleitung