Tomato juice inoculated with Cladosporium sp. or Penicillium sp. developed pH gradients with the upper portions near the mold mats having pH values near neutrality and the lower portions remaining more acid. Clostridium botulinum spores in these moldy tomato juices germinated, grew out, and produced toxin.

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A process for the aerobic biological decomposition of guayule (Parthenium argentatum Gray) prior to extraction of the rubber by mechanical means was patented by Spence (1933). The process, called retting because of the loose analogy to the retting of flax for the production of linen fiber, produced a marked decrease in the impurities of the rubber and improved the physical properties of the vulcanized rubber. It also decreased the resinous acetone-soluble contaminant from about 20 per cent of the crude rubber product to about 10 per cent, but no conclusions were drawn as to the agent responsible for the changes in composition and properties. The work reported in this paper is one phase of a reinvestigation of the retting of guayule by the natural microflora; it deals specifically with the decomposition of guayule resins. The resin of guayule is a mixture of acetone-soluble constituents of the plant. When the shrub is injured a clear resin exudes and dries. Other resin preparations were made by exhaustive extraction of guayule rubber with acetone and removal of the solvent. A variety of microorganisms normally present in the soil flora have been shown to oxidize compounds ordinarily considered relatively resistant to biochemical oxidation. Numerous species of bacteria have been found to oxidize phenols, and aromatic, alicyclic and aliphatic hydrocarbons. The literature on these subjects prior to 1940 is briefly reviewed by Bushnell and Haas (1941). Many species of actinomycetes oxidize aliphatic hydrocarbons (Umbreit, 1939) and the olefinic rubber hydrocarbon (

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