TRACHEID SIZE AND RATE OF ANTICLINAL DIVISION IN THE CAMBIUM OF CUPRESSUS

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Abstract
Differences of considerable magnitude occur in the tracheid dimensions of North American species of Cupressus. In general the species in arid regions (C. arizonica, C. glabra, C. forbesii, and C. macnabiana) have smaller cells than the species in more humid localities (C. macrocarpa and C. pygmaea). Minor, in some cases questionably significant, differences in cell size are found at different sites for the same species. Noteworthy interspecific differences exist in the frequency of anticlinal (pseudotransverse) divisions involved in cambial cell multiplication. On the whole, these divisions take place at a faster rate in the species with small cells (C. arizonica, C. macnabiana) than in species with large cells (C. pygmaea). Some general relationships between rate of growth, frequency of pseudotransverse divisions, and cell length are also evident. In the stems of mature trees, maximum cell length is apparently associated with a ring width of approximately 1–1.5 mm. Reduction in ring width is accompanied by a rise in frequency of pseudotransverse division and a slight recession in cell length. Widening of the rings produces no change in the rate of anticlinal division, in relation to linear radial accretion, but cell length declines. The orientation of the partition in pseudotransverse division is usually unidirectional in neighboring cells, but reversals in tilt occur after varied intervals. Duration of the interval between reversals shows an inverse relationship with the frequency of pseudotransverse division.