The variability in thickness of the O and A2 horizons was studied on a sandy loam forest soil in the Great Lakes‐St. Lawrence Region of southern Ontario. Horizon thicknesses were recorded in 1.3 cm (0.5 inch) classes for each 10.2 cm (4 inches) of horizontal distance on the faces of each soilpit. Soilpits were located both subjectively on windthrows and randomly in the study area. Thickness frequency distributions for O horizons were normal and for the A2 horizons Poisson‐like. Both were independent of recent fire history and sampling method. It may be inferred that the disturbance by windthrow is infrequent in relation to O horizon formation, but frequent relative to A2 horizon development. Microtopographic position had a slight effect; thicknesses in top positions being somewhat less than for bottom positions. Horizon distortions related to windthrow disturbance were recorded for only 19% of the soil profiles sampled.

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Studies of tree roots inevitably involve comparisons. While the norm is usually the natural root system we have little knowledge of the extent of genetic variation and control of root form for many of our species. The production of clonal material for experiments with tree roots seems necessary. Root form is discussed as it relates to: (1) cultural practices in the nursery and at outplanting, (2) modification by environmental factors, (3) changes in stand development and management practices, (4) the new forest and soil development. ResumeDes etudes d'enracinement appellent in6vitablement des comparaisons. Quoiqu'on utilise habituellement le systeme d'enracinement nature1 comme norme, nous connaissons tres peu I'etendue de la variation et du contrble genetiques de la forme de I'enrac~ne-ment de plusieurs de nos essences. La production de materiel de clBnes pour executer des recherches en enracinement semble donc necessaire. La forme d'enracinement est etudiee en quatre volets (1) les modes de culture en pepiniere et lors de la plantation (2) les variations dues aux facteurs ecologiques (3) les changements dans I'evolution du peuplement et des modes d'amenagement, (4) laforet nouvelle et I'evolution du sol.Any consideration of roots of planted trees involves comparisons. The usual standard of comparison is the same species as that under study but originating from seed in the outplanting area. But what of the genetic variation in root development within a species? More particularly, what is the capability within a species for it to respond to different growing conditions? We have evidence both from this meeting and elsewhere that seed origin or provenance and genetic control within a species can significantly affect root development. Foresters have observed variations in the aboveground form of trees that suited their purpose; in the field of fruit growing, the importance of the root stock has long been recognized. We have reached the stage in our investigation of the roots of forest trees where the use of general seed sources for experimentation is to be decried. The controls or standards used in our studies must be similar or identical genetically. The need for the large-scale operational production of clones of conifer species is obvious and, in my opinion, imperative. Without a high degree of certainty about the genetic similarity of the experimental material there will inevitably be anomalies and contradictory conclusions which will perpetuate myths and inhibit our clearer understanding of the factors governing forest growth.For Root Form as Influenced by Cultural Practices Either in the Nursery or at OutplantingThe majority of the papers have dealt with various aspects of roots as they are modified by cultural practices. There is a preponderance of studies dealing with container-grown seedlings and yet in North America and Europe the vast majority of trees produced for forest outplanting are still grown in conventional nurseries as bare root stock. Has the very act of growing trees in containers pu...

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