Plants are settled by epiphytic bacteriae able to convert tryptophan to IAA. This bacterial activity is abolished by chloramphenicol and streptomycin but not by penicillin. Tryptophan conversion to IAA by plant parts or enzyme preparations is far more intensive in non-sterile conditions than in sterile ones. This is true for all investigated objects: Helianthus annuus, Phaseolus vulgaris, Pisum sativum, Triticum vulgare, Zea mays, Enteromorpha compressa, Fucus vesiculosus, Furcellaria fastigiata. From pea plants, 58 strains of IAA producing bacteriae were isolated and partly identified.While non-sterile plants (Pisum, Zea) contain considerable amounts of IAA (extraction, thin layer chromatography, biotest), hardly any traceable auxin can be extracted of sterile plants. But sterile plants re-infected with mixtures or single strains of suitable bacteriae again contain considerable amounts of extractable IAA.

Using hydrocultured pea plants, 109 bacterial strains (42 from shoots) were isolated from shoots, roots, and from the hydroculture medium. 58 different strains (26 from shoots) were able to produce IAA from tryptophan, 15 different strains (7 from shoots) were able lo destroy IAA. (Included are 13 strains possessing both properties.) As far as they could be identified, the IAA‐producing and ‐destroying strains belong to Pseudomonas (by far dominating), Achromobacter, Alcaligenses, Bacillus, and Flavobacterium. The IAA‐destroying activity strongly depends on the physiological state of the bacteria and the milieu conditions. Bacterial IAA production (but not IAA‐degradation) is supposed to be important for the plant.

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Net photosynthesis and dark respiration of a natural Chara tomentosa community were continuously recorded. There is a close correlation between net rate of photosynthesis and variations in the PhAR flux under water. The net photosynthesis fluence Px correlates with the PhAR fluence Iz, but the quotient Px/Ix varies seasonally, apparently as a consequence of variations in chlorophyll content following long-range changes in radiation fluence. No influence of temperature, salinity or pH on net photosynthesis was detected, but water temperature stimulates dark respiration and consequently diminishes net primary production.