TRACHEID SIZE AND ANTICLINAL DIVISIONS IN THE CAMBIUM OF PSEUDOTSUGA

Abstract

This study is concerned with certain aspects of cambial behavior and tracheid size in Douglas-fir. Geographical origin of material was Colorado, Utah, Wyoming, Washington, and several localities in British Columbia from Golden to Vancouver Island. Tracheids were smallest in all dimensions in the Colorado collections and largest in wood from coastal British Columbia. In second growth trees 35–70 years old and 10–20 in. in diameter maximum cell length was associated with a ring width of approximately 1 mm, the length declining in both wider and narrower rings. Increase in girth was accompanied by pseudotransverse divisions, these occurring mostly in fusiform cells functioning as initials, and only rarely in derived xylem mother cells. At breast height the frequency of pseudotransverse division centered about a rate of 1.3 divisions per centimeter of xylem increment when rings were 2–7 mm wide. Reduction in ring width below 1 mm occasioned a rise in frequency of anticlinal division with consequent cell shortening. In the recent growth of old trees 475–675 years old and 3–7 ft in diameter similar relationships prevailed between frequency of anticlinal division, cell length, and ring width, but mean values for rate of division and cell length differed slightly from those for young trees. Upward in the bole, to a height of 50 ft, anticlinal divisions decreased in frequency and cell length increased, but the amount of cell lengthening was greater than could be accounted for by the change in rate of division. Notable differences in rate of division occurred between neighboring trees on most sites. Although pseudotransverse divisions took place at various times during the growing season, most were aestival. Length of the partition in pseudotransverse division, although fluctuating from cell to cell, was, in general, directly related to length of the cambial cell undergoing division. The orientation of the partition in anticlinal division was usually unidirectional in neighboring cells, but occasionally an indeterminate condition prevailed. When unidirectional, reversals in direction of tilt occurred after varied intervals. Duration of the latter tended to be inversely related to the frequency of pseudotransverse division.