Growth studies on the lactic streptococci: IV. Some observations on redox potential
Summary Redox potential changes at 30°C in anaerobic reconstituted skim-milk cultures of Streptococcus cremoris AM1 and AM2 and Streptococcus lactis ML8 have been investigated in batch cultures and continuous cultures maintained at constant pH by the addition of fresh medium. Str. lactis ML8 was more strongly reducing than either Str. cremoris AM1 or AM2. The positive Eh values which can arise in dense continuous cultures of lactic streptococci are not likely to affect either the lactic acid formation or proteolytic activity of the resultant bacterial concentrate. An electrolytic reduction cell is described which allows variations in redox potential in cultures to be controlled simply and effectively.
Oxidation-reduction potential and growth of Clostridium perfringens and Pseudomonas fluorescens.
A new apparatus was developed for measuring changes in E(h), pH, and cell numbers. With this apparatus, the relationships of these parameters were studied at initial E(h) levels of 200 and 40 mv (pH 7.0), by using Clostridium perfringens and Pseudomonas fluorescens. One of the strains of C. perfringens grew more luxuriantly at the higher E(h), in the presence of small quantities of oxygen, than at the lower one in the absence of oxygen. P. fluorescens could grow at a relatively low E(h) (40 mv, pH 7.0) in pure culture but not in the presence of C. perfringens under the same conditions.
The infection process, sporulation and survival of Alternaria helianthi on sunflower
SUMMARY 
 
Electron microscopy was used to study the infection of sunflower leaves by Alternaria helianthi. Conidia germinated by producing one to many germ tubes which grew across the leaf surface before forming appressoria. The fungus directly penetrated its host through the cuticle and epidermis. Entry into the host through wounds and stomates was also observed. Extracellular sheaths were found to be associated with germ tubes and intercellular hyphae of A. helianthi. Conidiophores developed through collapsed stomates, from leaf veins, trichomes and also from mycelium growing across the host leaf surface. Microcylic conidia were produced directly from parent conidia under certain conditions. Studies using a volumetric spore trap showed that the airborne spore concentration followed a distinct periodicity with peaks occurring between 0900 and 1100 h each day. Laboratory studies showed that safflower, noogoora burr and bathurst burr could serve as alternative hosts for A. helianthi. The pathogen was readily isolated from sunflower crop debris from a diseased crop that had been harvested 1 yr earlier.