UNITED STATES DEPARTMENT OF AGRICULTURE. FOREST SERVICE. FOREST PRODUCTS LABORATORY. MADISON, WIS PATTERN OF VARIATION OF FIBRIL ANGLE WITHIN ANNUAL RINGS OF PINUS ATTENURADIATA FPL-034 April 1964
PATTERN OF VARIATION OF FIBRIL ANGLE WITHIN ANNUAL RINGS OF PINUS ATTENURADIATA By CHARLOTTE H. HILLER, Technologist 1 Forest Products Laboratory, Forest Service U.S. Department of Agriculture Summary The variation of fibril angle within and between rings was investigated in 10-year-old trees of two Pinus x attenuradiata Stockwell and Righter clones. Within an annual ring, the fibril angles decreased from the beginning of the earlywood to the end of the latewood, following a linear trend. The fibril angles of the beginning of the earlywood tended to be larger than the angles in the latewood of the preceding annual ring. The trendwithinthe ring did not appear to be modified by the amount of latewood in the annual ring or by the width of the ring. Between the first six to eight annual rings from the pith, no significant radial trend was observed in the variation of the average fibril angles of the latewood or of the entire annual ring with the exception of one case where the trend was negative and parabolic. The fibril angles in compressionwood followed the same general trends of variation within and between rings. Introduction The fibril angles in the secondary cell walls of pine tracheids vary considerably within a tree, ranging from close to 0 to 45 or more. Undoubtedly, a large part of the variation is attributable to a multitude of internal and external factors which are difficult to separate. This variability is superimposed on systematic changes in angle sizes within and between annual growth rings. 1 Maintained at Madison, Wis., in cooperation with the University or Wisconsin. FPL-034
These latter patterns of variation of fibril angles have to date been explored more extensively in the latewood than in the earlywood because the fibril angles of the latewood are believed to have a greater influence on strength properties of wood. The fibril angles of latewood tracheids could also be measured more accurately by the method employed which was based on the inclination of checks 2 in the cell wall and of pit apertures in the cross field. So far the following patterns of variation of fibril angles Rave been discovered in the latewood of some of the yellow pines. 2, 3, 4 Within an annual ring, the fibril angles decrease in the radial direction from the beginning to the end of the latewood. The relationship between the average latewood fibril angle and the consecutive annual rings from the pith is curvilinear; the fibril angle decreases in consecutive growth rings from pith to bark until a certain point is reached beyond which the angle becomes relatively constant and shows only slight fluctuations. The point at which the angle becomes constant varies with the growth rate of the tree. The same curvilinear trend is observed from the apex to the base of the tree when the increment sheath of a given calendar year is sampled at the midpoint of consecutive annual height increments. The fibril angles of compression wood tracheids are always as large or larger than the fibril angles of normal latewood tracheids at the same relative position in the tree. Apparently they do not decrease in size in the radial direction within a growth ring, but there are indications that they follow the same trend as the fibril angle of normal wood in consecutive annual growth rings from pith to bark. The decrease in angle size, however, is not as pronounced as it is in the normal latewood. It is generally accepted that the fibril angles of earlywood tracheids are larger and vary over a wider range than those of latewood tracheids in the same annual ring; however, it seems that the pattern of variation of the earlywood fibril angles has not been examined in detail. This study, therefore, was undertaken to examine and compare the patterns of variation of the earlywood and latewood fibril angles within and between annual rings. 2 Pillow, M. Y., Terrell, B. Z., and Hiller, C. W. Patterns of variation in fibril angles in loblolly pine. U.S. Forest Products Lab. Rpt. 1935. 1959. 3 Hiller, C. H. Variations in fibril angles in slashpine. U.S. Forest Products Lab. Rpt, 2003. 1959. 4 Hiller, C. H. Correlation of fibril angle with wall thickness of tracheids in summerwood of slash and loblolly pine. Tappi 47(2):125-128, Feb. 1964. FPL-834-2-
A sample with compression wood in all of its annual rings was included in the investigation to obtain additional information on the variation of the fibril angle in this type of wood. Material Used The material was chosen so that the consistency of any pattern of variation of the fibril angle that might be formed could be tested on genetically homogeneous material subjected to different environments. The samples were increment cores obtained from the Institute of Forest Genetics, Placerville, Calif. The cores were taken from two clones of Pinus x attenuradiata Stockwell and Righter, the hybrid of knobcone pine ( Pinus attenuata Lemm.) and Monterey pine ( Pinus radiata D. Don). The clones represented the F generation of wind pollinated F hybrids. A 2 1 total of 12 trees were sampled, 7 belonging to 1 clone and 5 to the other one. The trees, started from cuttings in October 1946, were all of the same age and had been grown in the same general area. The individual trees of each clone, however, had been planted in different blocks. Thus, the two groups of trees available for study were genetically homogeneous within the group so that any differences between the trees in a clone were probably caused by random environmental influences. Consistent differences between the two clones, on the other hand, could be due to different genetic makeups. From each tree oneincrement core was taken from 3 to 5 feet above the ground at the end of the 1956 growth period. The cores had a diameter of 3/16 inch, and consisted of the pith and 7 to 9 annual growth rings from pith to bark. In the southern pines, investigated previously, 2, 3 the average latewood fibril angle decreased rather rapidly in consecutive rings close to the pith. It seemed advisable, therefore, when comparing the fibril angles of annual rings from different trees, that rings should be at the same relative position from the pith and formed in the same calendar year. Otherwise, effects of position in the tree and environment would be confounded, and it would be difficult to attribute differences in fibril angle sizes or in patterns of their variation to either one of those factors. Consequently, the increment cores were segregated accordingto clone, number of annual rings from the pith, and calendar year of ring formation as follows: No. of No. of rings Calendar year Clone trees from pith to bark of ring formation 107 3 9 1948-1956 107 4 8 1949-1956 4 5 7 1950-1956 FPL-034-3-
The first and the last annual rings of each core were not measured. The first ring proved unsuitable for fibril angle measurements because it has so little latewood, and the last ring, formed in 1956, was found to be incomplete. Method of Fibril Angle Determination The fibril angles were determined by measuring the angle formed by checks and elongated pit apertures with the longitudinal axis of the cell. The determinations were made on the split radial surface of the cores with the aid of fluorescence 5 microscopy. The method has been developed and described by Marts.-It was chosen in preference to a method that employs the light microscope, because the angles could be measured directly on the radial surface of the cores without the necessity of preparing slides. Furthermore, there are no elongated pit apertures in the earlywood, and the fibril angle must be estimated by measuring the angles of checks in the cell wall. Marts' procedure reveals these checks more clearly. In order to discover their pattern of variation within an annual ring, the fibril angles were determined and recorded in the sequence in which they naturally occur from the beginning to the end of the growth ring. The width of each ring was measured in millimeters under the microscope with the horizontal vernier of a graduated mechanical stage; the ring was divided radially into quarters, and five. angles were measured at random in each quarter or zone, giving a total of 20 determinations for a ring. Because of the great variability of the angles in each quarter, it would have been desirable to make more measurements; however, five well-defined checks were generally the maximum number that could be found in an earlywood quarter of an annual ring. The boundary between earlywood and latewoodin an annual ring was also noted so that the average angles of the two tissues could be computed. Results and Discussion The variation of the fibril angle within annual rings is shown for each tree in the two clones (figs. 1, 2, 3). The five trees of clone 4 are represented in figure 1, the four trees of clone 107 with eight rings from the pith in figure 2, and the three trees of clone 107 with nine rings from the pith in figure 3. The between-clone variation is shown in figure 4. Annual rings and latewood zones are drawn to scale. 5 Marts, Ralph O. Fluorescence microscopy for measuring fibril angles in pine tracheids. Stain Technol. 30(5):243-248, Sept. 1955. FPL - 034-4-
Generally speaking, there is no evidence that the relationship between zones and fibril angles is anything but linear. The fibril angles in the majority of the rings start at a relatively high point in the earlywood and then decrease toward the latewood. Usually, the mean fibril angle of the first earlywood zone is higher than the mean angle of the last zone of thepreceding ring. The latewood does not seem to affect the general trend already established in the earlywood. In figure 4 all the trees in a clone have been averaged so that the sample number, on which the means of each zone are based, has been increased. The result is a more obvious negative relationship between zones and fibril angles in most rings. (The range of fibril angles seems to be larger in fig. 4 because the scale has been expanded as compared with the scales in figs. 1-3.) No differences between clones are apparent with respect to this general trend of fibril angle variation within the ring. As previously mentioned, the variation of the fibril angle in consecutive rings from the pith has been studied in previous investigations always with respect to the average fibril angle of the latewood. In this investigation, both the average fibril angle of the latewood and of the entire annual ring were computed in order to determine if the pattern of variation would be different when the fibril angles of the earlywood are taken into account. Figure 4 shows that the mean fibril angles are large in all annual rings and decrease very little in size with the number of rings from the pith as compared to the southern yellow pines that have been examined previously. 2, 3 The mean fibril angles of the latewood are, in general, smaller than the mean angles of the entirering, but the relationship between the fibril angle and the consecutive annual rings from the pith seems to be the same for the two means. The tree sample with compression wood is shown in figure 2. In the compression wood the fibril angles seem to be less variable within the zones than the fibril angles of the other trees in this group. However, the pattern of fibril angle variation within and between rings of the compression wood sample does not differ from that of the other trees so that the former was included in the analysis of variance. Similar results were observed on Pinus elliotti Engelm. ( Pinus caribaea morelet). 6 The conclusions concerning the trends of fibril angle variation, arrived at from the graphs, were confirmed by statistical analysis (table 1). The clonal groups were analyzed separately because of the difference in the number of annual rings between the groups. A split-plot analysis was used. The analysis of the three trees 6 Schmidt, J. D. K., and Smith, W. J. Wood quality evaluation and improvements in Pinus caribaea morelet. Queensland Forest Service Research Note No. 15. Dept. of Forestry, Brisbane, Austrailia. 1961. FPL-034-5-
in clone 107 is the only one that shows significant differences between trees and between annual rings. This result is probably due to the one very narrow-ringed tree that differs considerably from the other trees in the rate of decrease of the fibril angle in consecutive rings from the pith and in the average fibril angle of the entire tree (fig. 3). The nature of the relationship between fibril angles and annual ring number from the pith was explored by partioning the sums of squares for rings into linear, quadratic, and cubic components. A significant quadratic trend was found only in the group of three trees of clone 107. In all three groups the difference between zones is significant. Most of the difference is accounted for by a negative linear regression. The interaction of annual rings and zones is also significant in both groups of clone 107 indicating that in these cases the zonal differences varied with the relative position of the annual ring in the tree. The graphs in figures 1 to 3 seemed to indicate a correlation between ring width and the rate of decrease of the fibril angle within the ring. To test this relationship, annual rings formed by trees in a clone at the same position from the pith were selected at random and the regressions of the fibril angles on zones were computed for the individual rings. An examination of the regression coefficients of rings differing in width disclosed no relationship between the rate of decrease of the fibril angle within a ring and ring width. Neither was there a relationship with position of the annual ring in the tree. The results of this study are, of course, applicable only to young trees of Pinus attenuradiata. The lack of between-ring variation of the fibril angle in annual rings close to the pith seems to be peculiar to the species. Older trees and a longer series of consecutive rings from the pith should be studied to determine if the same condition prevails throughout the series. The influence of such factors as ring width should also be studied on more rings and rings of different ages. The same is true of the within-ring variation of the fibril angle. It should be further examined in annual rings at a greater distance from the pith because of the difference in anatomy of rings in juvenile and mature wood. Annual rings at a greater distance from the pith probably do not only contain more latewood than the material studied, but latewood that is composed of thicker walled and longer tracheids. These conditions may very well affect the trend of the fibril angle variation within the ring, especially if the latewood differs considerably in these anatomical features from the earlywood in the same ring. Previous studies have established close correlations between the fibril angle and tracheid length as well as cell wall thickness. 3, 7 7 Echols, R. M. Linear relation of fibrillar angle to tracheid length, and genetic control of tracheid length in slash pine. Tropical Woods (102):11-22, 1955. FPL-034-6- 2.-13
Table 1.--Analysis of variance testing the influence of trees, rings, zones, and their interactions on the fibril angle in two clones of Pinus attenuradiata
Figure 1.--Within-ring variation of fibril angles (rings 2-6). in five trees of Pinus attenuradiata (clone 4).
Figure 2.--Within-ring variation of fibril angles (rings 2-7) in four trees of Pinus attenuradiata (clone 107).
M 124 248 Figure 3.--Within-ring variation of fibril angles (rings 2-8) in three trees of Pinus attenuradiata (clone 107).
Figure 4.--Within-ring variation of fibril angles (rings 2-8) of Pinus attenuradiata (clones 4 and 107).
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