IAWA Journal, Vol. 20 (4), 1999: 405-417 RAYS IN JUVENILE WOOD OF ACER by J.E. Dakak l , R. Keller l & V. Bucur 2 SUMMARY Juvenile wood characteristics of multiseriate and uniseriate rays of five species of the genus Acer were studied on young trees from France and Canada. Ray height, width, number in width of cells and proportion/ mm2 were determined for the earlywood. Variance analysis was used to discriminate the variability of the characteristics of rays. Simple regres­ sion analysis shows some strong correlations between the character­ istics of multiseriate and uniseriate rays of each species. Except for A. saccharinum, no relationships were established between the ray char­ acteristics and the specific gravity. Except for A. pseudoplatanus, no relationships were established between annual ring width and ray char­ acteristics. Principal component analysis focused separatelyon multi­ seriate rays and on uniseriate rays revealed differences between A. sac­ charum and A. saccharinum (e.g., the proportion and the number of cells in multiseriate rays). Key words: Ray size, juvenile wood, earlywood, Acer campestre, Acer platanoides, Acer pseudoplatanus, Acer saccharum, Acer saccharinum. INTRODUCTION Anatomical descriptions of maple wood (Acer) are available in numerous reference books (Greguss 1945; Stark 1954; Jacquiot et al. 1973; Wagenführ 1974; Core et al. 1976; Butterfieid & Meylan 1980; Panshin & de Zeeuw 1980; Koch 1985). Rays in Acer are homocellular, uniseriate and multiseriate. In hard maples there are rays of two distinct widths. The size and distribution of rays and vessels in hardwoods affect wood quality and utilization, both for solid wood and paper and pulp. Wood figure in maple is related to the size and distribution of rays. The ray cells are short and usually thin-walled and so contribute little to the strength properties of paper. In solid wood the ray tissue con­ tributes to acoustic wave propagation in radial direction (Bucur 1995). In the U.S. sugar maple (Acer saccharum Marshall) and black maple (Acer negundo L.) are sold as hard maple. Soft maples, e. g. Acer rubrum L. and A. saccharinum L., 1) Ecole Nationale du Genie Rural des Eaux et Forets, LRSF, 14 rue Girardet, F-54042 Naney, Franee. 2) Universite 'Henri Poineare', Faeulte des Seienees, LERMAB, BP 239, F-54506 Vandoeuvre les Nancy, France. Correspondenee to be addressed to V. Bueur, e-mail: [email protected] Downloaded from Brill.com09/30/2021 05:39:25PM via free access 406 IAWA Journal, Vol. 20 (4), 1999 are distinguished fromAcer macrophyllum Pursh in that "the rays intergrade in size in these last-named species and the widest rays are not so broad" (panshin & de Zeeuw 1980). Ray width is considered a useful character for wood identification of species groups of the maple group (Acer spp.). Ray characteristics of five Acer species are given in Table 1. n is generally accepted that the juvenile wood is characterized by shorter elements and a higher microfibril angle when compared to the mature wood (pans hin & de Zeeuw 1980; Koch 1985; Zobel & Sprague 1998). As noted by Zobel (1981), Zobel and Jett (1995), and Zobel and Sprague (1998) the juvenile wood of temperate-zone diffuse-porous species is not markedly different from mature wood. Fukazawa (1984) suggested that juvenile wood in hardwoods can be defined as "a region up to 5-8 cm from pith, regardless of their growth rate." These words noted that the effect of growth rate on juvenile wood properties of diffuse-porous hardwoods generally is relatively small. Table 1. Some characteristics of rays of Acer species, as noted by the literature. Characteristics of rays References width height total no. 11m nO.of 11m nO.of of rays author with year cells ceIIs permm2 Acer campestre - Field maple 30-60 1-5 <500 Keller 1992 1-6 1-40 50-60 Gregus 1945 30 2-4 320-800 Freund 1970 Acer platanoides - Norway maple 40 1-5 10-40 Keller 1992 53 4-6 470-600 Freund 1970 1-3 60-70 multi 10-12 Greguss 1945 uni 16-18 Acer pseudoplatanus - Plane tree maple 40-80 1-8 > 1000 60 Keller 1992 1-3 1-60 50-60 Greguss 1945 56 5-8 480-1000 Freund 1970 17-74 122-765 Tabatabi et aI. 1962 480-1000 Schmidt 1941 Acer saccharum - Sugar maple 3-8 multi> 800 Panshin 1980 uni> 200 19-53 1218 Stark 1954 Acer saccharinum - Silver maple 1-3 1-70 80-90 Greguss 1945 20-27 3-4 612-812 41-59 Stark 1954 Downloaded from Brill.com09/30/2021 05:39:25PM via free access Dakak, Keller & Bucur - Rays in Acer 407 In recent years, in North America and in Canada, a strong attack of Ceratocystis on Acer saccharum wood was observed. This attack can be avoided by drying the wood to a moisture content below 20%; A. saccharinum is not attacked by this fungus. Acer saccharum and A. saccharin um have a very similar anatomical structure and be­ cause of this it is very difficult to differentiate them macroscopically. Information is available on the rays of A. saccharum, A. saccharinum (Stark 1954; Koch 1985), and A. pseudoplatanus (Vasiljevic 1951). The importance of A. saccharum andA. saccha­ rinum wood is increasing, especially in the U. S., because of increased use of these species for veneer, furniture, flooring, etc. To our knowledge, no references were pub­ lished on the ray characteristics of young wood of Acer species of European origin. The aim of this research is to study the characteristics of rays in juvenile wood of Acer campestre L. (field maple), A. platanoides L. (Norway maple), A. pseudoplatanus L. (Plane tree maple), A. saccharum Marshall (sugar maple), and A. saccharinum L. (silver maple), and to further establish useful criteria for identification of different maples, especially A. saccharum and A. saccharin um. MATERIALS AND METHODS The investigations were conducted on young trees (diameter between 6 and 16 cm) from East France, Lorraine (A. campestre, A. platanoides, A. pseudoplatanus) and East Canada (A. saccharum, A. saccharinum). From each species three individuals were taken. In each tree, at 1.30 m height, one disk of 10 cm thick was cut. From this disk five sampIes (small wood blocks, 20 x 20 x 40 mm), located between the 15 th and the 20th annual ring, were prepared as microscopic specimens in longitudinal tangen­ tial plane of wood and for other physical properties measurements (basic density and annual ring width). For microscopic observations (Freund 1970), the blocks were embedded in polyethylene glycol 1500. The ray characteristics of the 15 th ring were analyzed. The microscopic sections measured 15 mm x 7 mm x 12 J.Ull. Five rnicro­ scopic fields were explored for each section, one located in the center and four 10- cated in each corner. All the microsections were located in the earlywood zone of the 15 th juvenile annual ring. More than 30,000 measurements were taken to characterize the rays. Photomicrographs (Dakak 1997) were taken from each field of the micro­ scopic sections stained with safranin and mounted in Canada balsam. Measurements were perforrned using a Zeiss optic microscope equipped with a camera. The following characteristics of rays (uniseriate and multiseriate) of the earlywood were measured on a reference microscopic surface of 1 mm2 of each sec­ tion: • height of ray in J.Ull (H for multiserate rays and h for uniseriate rays). Rays wider than three cells were considered multiseriate; • width of ray in mm (L for multiseriate rays and 1 for uniseriate rays); • number of cells in a ray at maximum width (N for multiseriate rays and n for uniseriate rays); • ratio between area of rays and the observed surface in % (P for multiseriate rays and p for uniseriate rays). Downloaded from Brill.com09/30/2021 05:39:25PM via free access 408 IAWA Journal, VoL 20 (4),1999 The number of rays was manually counted in the microseopie screens of 1 mm2 in tangential longitudinal seetion of each growth ring. Specific gravity (s.g.) was based on green volume and ovendry weight and was expressed in kg/m3. The annual ring width (w) is expressed in mm, and represents the average annual ring width between the 15 th and 20th ring, assumed to be part of the juvenile wood zone. For statistical analysis, routine linear regression analysis, analysis of variance (ANOVA) and principal component analysis were used with SAS/Stat 1999 to study the variability of the population. Table 2. Ray characteristics in juvenile wood of studied Acer. Characteristics of rays Values Multiseriate rays Uniseriate rays H L H/L N P h h/l n p 11m 11m % 11m 11m % I. Acer campestre minimum 254 27.5 8.6 4.0 1.8 10.8 12.4 0.7 1.5 6.1 average 344 32.3 10.7 4.1 7.5 90.9 14.1 6.5 1.7 8.0 maximum 397 37.7 12.l 4.6 14.3 129.0 15.6 8.4 1.9 12.1 C.v. % 13 9 13 6 50 40 9 36 8 28 2. Acer platanoides minimum 372 34.0 7.6 4.2 5.3 81.0 11.0 7.1 1.3 1.8 average 432 42.3 10.5 4.8 8.8 113.0 14.0 8.0 1.6 4.3 maximum 579 57.0 13.8 5.5 12.4 140.0 16.6 8.9 2.0 6.8 c.v. % 15 20 23 9 28 18 14 7 16 40 3. Acer pseudoplatanus minimum 64 32.5 1.9 4.0 0.6 77.9 1.6 6.3 1.2 1.4 average 27 49.4 5.1 5.5 5.6 116.0 11.5 16.4 1.4 6.3 maximum 366 59.7 7.l 6.6 16.0 139.0 15.1 75.0 1.6 11.0 C.v.