Tracheid size and rate of anticlinal divisions in the cambium were determined for lodgepole pine at several sites in western North America ranging in elevation from 3000 to 11,000 feet. The determinations were made at breast height in trees with boles 10ndash;20ensp;in. in diameter. The base rate of anticlinal division was low as compared with other conifers, the average being 0.8 divisions per cm of xylem increment when ring width exceeded 1.5ensp;mm. The frequency of division increased as annual xylem production fell below 1ensp;mm, and rose sharply with continued reduction in ring width under 0.3ensp;mm. Maximum cell length was associated with a ring width of 1ensp;mm, and the length decreased in both wide and narrow rings. The tangential width of the tracheids likewise lessened as ring width fell below 1ensp;mm, the decline becoming accentuated with continued waning of growth to less than 0.3ensp;mm. Cell diameter differed from the overall mean by more than 1ensp;micro; at only one site after allowance was made for dissimilarities in growth rate. Cells were shortest at the two highest sites. The newly formed partition in pseudotransverse division tended to be inclined in the same direction in neighboring cells, but the percentage of divisions deviating from the preferred orientation was higher than in other conifers. Reversals in direction of tilt occurred after varied intervals, these apparently being corrective in function.
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