METHODS OF OBSERVING SOIL FLORA AND FAUNA ASSOCIATED WITH ROOTS

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Abstract
Organisms associated with living roots may be observed at magnifications up to 900 diam. when roots are grown in soil against glass coverslips. Such coverslips may serve as bottoms of small dishes, or be cemented over openings cut in glass or brass sides of miniature observation boxes of a type described earlier. Objectives found useful are apochromatic, up to 10 X; achromatic 20 X and water-immersion 40 X; and apochromatic 90 X oil immersion. The last requires a large immersion drop and a strong beam of light at a low angle. Illumination is from a 100-watt lamp in a housing with adjustable condensers, cooled by passage through water, and brought to a sharp focus with a strong plano-convex lens or a spherical flask of water. In prepn. for observation by transmitted light, loss of organisms from a root surface is minimized by fixing in formalin-acetic-alcohol without washing, clearing in hot lactophenol, then staining briefly by adding acid fuchsin to the lactophenol. These methods reveal abundant bacteria, motile and in colonies, on very young epidermis and root hairs; also fungi, protozoa and nematodes. The author regards as inadequate the view that activity in the rhizosphere is related chiefly to destruction of senescent root cells.

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