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SUMMARYThe roots of 36-year-old Donglas firs were sampled in a stratified random fashion with a Veihmeyer-type auger. The lengths of root were very variable as was the proportion of fine roots which were dead. From consideration of the possible causes of spatial variability, it was concluded that it was not due primarily to environmental variation, nor to position relative to the tree trunks and crowns except for concentrations adjacent to the trunks where stem fIow is considerable. Cyclical initiation, extension and death of fine roots in a spatial pattern with cells perhaps as small as 30 cm diameter could explain the observations. A drought period might have caused more extensive death of fine roots on one of the three plots examined.

Twelve fluorescent dyes were tested in the laboratory for their stability under conditions of alternate wetting and drying, and persistence of fluorescence in the presence of an acid soil. The strongly fluorescing Pyranine conc. was most suitable for tracing water percolating through soils. In the field this dye could be detected in the soil after several months and could be photographed in ultraviolet light. The greater percolation of water against tree trunks and lateral movement in the humus layer were demonstrated.

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