Douglas Fir Fiber 673 



Microscopic Characteristics of Fiber' 



As is shown in Plate 1, Figure 2,' which includes one spring, 

 one intermediate and one summer fiber, the average tracheids of 

 Douglas fir are roughly one himdred times as long as they are 

 broad, and are more or less pointed at the ends. In length there is 

 much variation, depending on the position of the fiber in the tree. 

 In the wood formed around the pith the fibers are less than one 

 third as long as the average, as may be seen from comparison of 

 Figures 1 and 2, Plate 1, in which are shown mature and first an- 

 nual ring fibers on the same scale of magnification {see also Tables 

 and Curves). According to studies made by Miss Gerry (3) the 

 fibers in the early or springwood of any given annual ring are 

 longer than those in the late or simimerwood. Our measure- 

 ments show no great difference in the average length of the fibers 

 of the springwood and those of the summerwood. There is, how- 

 ever, an indication that the fiber of the summerwood is slightly 

 longer, as may be seen in Table IV and as is illustrated in Plate 1, 

 Figtire 1. The shortest fibers of the sirmmerwood are those last 

 formed, in the springwood the location of the minimum fiber ap- 

 pears to be more irregular. According to PenhaUow (5, p. 360), 

 in width the tracheids of Douglas fir are about .03 mm in early 

 wood, and .027 mm tangentially or .018 mm radially in late wood. 

 The actual walls are about .0024 mm thick in the springwood and 

 .0084 mm thick in the simmierwood, i. e., they are some three times 

 as thick in the late as in the early wood. We have made no 

 special study of the thickness of the walls. 



' The terms fiber and tracheid are used interchangeably throughout this 

 discussion. 



' Description of Plate 1. 



Fig. 1. — Fiber from the first annual ring of Douglas fir, shipment 2, tree 1, 

 disc X. Stain nigrosin, mounted in balsam, x 20. 



Fig. 2. — One springwood, one summerwood, and one intermediate Douglas 

 fir fiber from ring 152 years from pith, shipment 2, tree 1, disc B. Stain 

 Haidenhain's haematoxylin, mounted in glycerin jelly, x 20. 



Fig. 3. — "Rotholz" fiber, showing spiral striations, from same mount as 

 figure 1. X 100. 



Fig. 4. — Part of single springwood fiber of Douglas fir, shipment 2, tree 1, 

 disc F, last annual ring, showing the characteristic tertiary spiral thickenings. 

 Stain nigrosin, mounted in balsam, x 285. 



Fig. 5. — Another part of same fiber as shown in figure 4, showing the 

 crossing-field of the ray. Note the three smaller marginal pits at both the 

 top and the bottom of the group of larger pits, x 285. 



Fig. 6. — Another part of the same fiber as shown in figure 4, showing 

 bordered pits, x 285. 



Photomicrographs by Mr. W. B. Stokes, Forest Products Laboratories of 

 Canada, Montreal. 



