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The monoterpenes from needles of 47 adult trees of Picea abies (L.) Karst., grown under natural conditions, were studied to get information about the tree-to-tree variation within three adjacent locations and the differences between the locations. For the absolute amounts of the monoterpenes the tree-to-tree variation ranged between 50% and 70%, expressed as the relative coefficient of variation. All three populations showed similar variations. When looking for different genotypes, at each location two groups of trees were observed, which were characterized by the ratio of myrcene to limonene.

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The interaction between the roots of Zea mays L. and its rhizosphere microflora was studied in nutrient solution with respect to two exemplary aspects ‐ water soluble vitamins and the four most frequent carbohydrates. The exudation of vitamins and sugars into the medium is increased in a solid substrate (glass‐ballotini simulating soil structure) in comparison with nutrient solution only. The amounts of vitamins released (1 to 421 ng per plant) are high enough for a pronounced influence on the rhizosphere microflora to be expected. However, the microbial population feeding on the exudates has very simple nutritional demands. In spite of appreciable amounts of vitamins found in the inoculated nutrient solution, the growth of vitamin requiring species is not stimulated compared to the soil population. The roots are mostly inhabited by shorter rods and occasionally by actinomycete‐like filaments. The percentage of the root area covered by its microflora, assuming a monolayer, is 4% in the root region where root hairs are just emerging, 7% in the root hair zone and 20% in the oldest part of the roots, 10 mm below the grain. In the presence of rhizosphere microorganisms, root dry weight is lower than that of axenically grown plants because the diameter of the primary root is diminished. In addition, the vitamin and sugar content of the root is affected by rhizosphere microorganisms. The results can be interpreted as an indication that phytohormones may participate in interactions between roots and bacteria.