Faculty of Agriculture, Alexandria University ,

Alexandria , Egypt , and

and

H.I. El-Mously

Dept. of Production Engineering

Faculty of Engineering

Ain-Shams Univ. , Cairo

Egypt .

* This paper was presented at the IUFRO XX World Congress, Project Group P5.04, August 6-12, 1995 , Tampere , Finland . 

INTRODUCTION

The date palm ( Phoenix dactylitera L.) is an important crop grown in Egypt and Arab countries. The estimated palm population in Egypt is more than 10 million trees.

The large number of date palm trees growing in Egypt provide a very large quantity of non-fruit materials, e.g. frond basis, rachis (frond midrib), leaflets (lamina), spadix stem (axis), spadix fruit stalks (branches) and date palm fibers. These materials are used locally in some products such as vegetable and fruit baskets and other containers, cheap furniture ,roofs of village houses, and as a fuel.

Recently, the Center for Development of Small Scale Industries and Local Technologies has demonstrated, through a number of research projects, a successful use of date palm fronds for the manufacturing lumber-core plywood (blockboard), arabesque, parquet and as raw material for particleboard.

The properties of palm frond products as biological raw material are mainly determined by its structure. The general anatomical description of palms was given by Tomlinson (1961). The distribution of the vascular bundles across the stem was studied in other monocotolydons plants (Grosser and Liese 1971). However, the knowledge of the palm fronds anatomy is still rather limited even qualitative or quantitative. The aim of this investigation is to provide the basic description of anatomical structure of palm leave's midrib (palm fronds) and the variability of structure quantitatively (fiber length, number of vascular bundles, percentage of fiber tissue, distribution of vascular bundles in different locations of frond and thickness of periphery vascular sheath).

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MATERIAL AND METHODS

The material for this investigation was collected from two governorates :

1. From Giza governorate for anatomical description and percentage of fibers across the section.. Two varieties of palm were taken, namely, Seiwi and Baladi. These two varieties are widely distributed in Egypt .

2. From Aswan governorate for determination of fiber length and fiber diameter.Two varieties of palm were taken, namely, Baladi and Zokor (males).

The fronds were divided into three equal parts. A 5 cm long disks were cut from the middle of each part. The specimens were killed and fixed in FAA.

For microscopic studies, a 5 mm thick blocks were taken in sequence from the surface to the center of the disk and embedded in polyethylene glycol (PEG) according to Weiner (1992). About 30-50 .microns thick transverse and longitudinal sections were cut on a sliding microtome and stained with safranin and.fast green.

The percentage of tissues were estimated in the cross sections .by using stereological techniques based on counting of points and intersections for microscopic images on screen of projection microscope according to Ifju (1983).

Vascular bundle diameter was measured along the direction of maximum diameter (Bhat et al. 1993). Number of vascular bundles per .mm2 was measured in radial positions using projection microscope. Fiber length was measured on sclerenchyma cells macerated by Franklin method. The chips of palm fronds were taken from different zones across and along the frond and macerated in a mixture of equal volumes of glacial acetic acid and 30% hydrogen peroxide at 60°C for 24-48 hrs. Macerated fibers were stained in safranin. Fiber length were measured to the nearest 0.01 mm. Lengths of 50 whole fibers of macerated tissue from each sampling location were measured. This number of fibers was based on calculations of preliminary sample size determination with desired error of 0.1 mm. The data were statistically analyzed using general linear model procedure (GLM) (SAS).

RESULTS AND DISCUSSION

The anatomical structure of palm leaves midrib Palms do not possess cambium and hence their "wood" is primary and is not comparable in developmental terms to the wood of dicotyledons and gymnosperms which is mostly secondary xylem.

The anatomical structure of palm leaves midrib corresponds to the general structure of stems of monocotyledons, represented by collateral vascular bundles embedded in ground parenchyma (Fig. 1).

The cuticle layer is distinct and the epidermal cells are mostly single layer followed by the cortex.

The cortex between epidermis and the vascular system consists of parenchyma cells. Fibers (sclerenchyma) and incomplete vascular bundles (Fig. 2). The width of the cortex varied the base of the frond to the top. Generally, the cortex in the top is relatively wider (Fig. 3). The parenchyma cells in the cortex are mostly silicified. Xn the top of the frond the cortex layer contains columnar (radially elongated) cells. These cells contains chloroplasts(Fig. 3).

As in rattan palm stems (Meiner and Liese 1990), the central cylinder begins with the first fully developed vascular bundles which from a complete circle (Fig. 5).

The vascular bundles consist of the conducting tissue, phloem and xylem. and fibers which provide structural support (Fig. 5).

The xylera consists of protoxylem and metaxylem (Fig. 5). Protoxylem consists of small narrow xylem elements (vessels) with average diameter of 20 microns. The metaxylem consists of 1-4 layer xylem elements (Figs 1, 2, 3, 4, and 5). The diameter of metaxylum vessels ranged between 70 to 180 microns (larger diameter). All the vessels are surrounded by iignified parenchyma cells.

The phloem consists of large, thin-walled unlignified sieve tubes, always connected with several companion cells (Fig. 5). At the periphery of phloem there is a layer of compressed cells belonging to the primary phloem.

The phloem and xylem of vascular bundle are each surrounded by sclerenchyma sheaths (fiber). Besides, the fibers consists a separate strands on inner and outer side of the vascular bundle (Fig. 5). Sometime, specially on the outer zone, fiber composed a complete sheath around the vascular bundle. The size and shape of fiber strands in the vascular bundle appears to be the most important structural factor that determines the palm leaves midrib behavior.

The ground parenchyma is composed of thin-walled, large and round with relatively small intercellular spaces.

Variability of vascular bundles across palm leaves midrib The distribution of the vascular bundles across the midrib is consistent with the typical monocotyledon stem anatomy (Parthasarathy 1976). Form, size number of bundles change continuously from the periphery of the midrib towards the center (Table 2 and Pigs. 6, 7 and 8).

Across the midrib (Table l and Figs. 8) the vascular bundle diameter increase rapidly to about 1-2 mm and then the diameter slightly fluctuated to the center of midrib.

Near the periphery, the bundles are smaller (the average diameter is 0.34 mm) and more numerous (the average No. of vascular bundles per mm2 near surface is 4.5) so that there are only a few parenchyma cells between them ( Table 2 and Figs 2, 3, 4, and 5). The vascular bundles in the outer part of the midrib are circular in cross section and with one or two metaxylem tissue and fiber sheath almost united with the sclerenchyma of the cortex (Figs 2 and 7).

Towards the center of the midrib the vascular bundle become bigger, oval and more distributed (table 2 and Figs 2,6 and 7).

Across the midrib, three zones of vascular bundles can be distinguish (Figs 2, 4, and 7). The first, the peripheral zone is composed of vascular bundles immediately adjacent to the cortex and they are arranged generally in more or less tangentially orientated chains. In the second zone, the transitional zone, the fiber sheath is thick, and the vascular bundles are numerous with small parenchyma ceils between them. The third zone (Figs. 6 and 7) is the broadest, where the bundles reach their highest stage of differentiation and highest diameter. In the inner zone of third zone (near center) a very small bundles are distributed among the big vascular bundles (Figs. 6 and 7). This distribution are similar to the monocotoedonous plants. In bamboos, Grosser and Liese (1971), distinguished four zones of vascular bundles across the culm-wall.

The periphery and transition zone across the midrib which is characterized by higher percentage of fiber tissue and larger number of bundles affect the density and strength properties of diameter of fibers are smaller in Zokor fronds. Along the frond, the fiber length is lower in the middle part of the frond than base and the top (Table 3).

The average fiber length in palm midrib (1.325) is within the averages of dicotyledons and hardwoods and shorter than the fiber length of the stems of some other palm species as rattan (Bhat et al. 1993).

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REFERENCES

Bhat, K.M., K.M. Mahmamed Nasser and P.K. Thulasidas 1993. Anataty and identification of South Indian rattans {Calamus species).

IAWA Bull. n.S. 14(1); 63-76. Grosser D. and W. Liese 1971. On the anatomy of Asian bamboos, with special reference to their vascular bundles. Wood Sci. and Technology 5; 290-312.

Xfju,G. 1983. Quantitative wood anatomy. Certain geometrical- • statistical relationships. Wood and fiber Sci. 15 (4); 326- 337.

Parthasarathy, M.V. and L.H. Klotz. 1976. Palm "Wood". I. Anatomical aspects. Wood Sci. and Technology 10: 215-229.

Tomlinson. P.B. 1961. Anatomy of Monocotyledons. II. Palmae. Clarendon press, Oxford

Weiner, G. 1992. Zur Stammanatomie der Rattanpalmen . Ph.D.Thesis, Univ. Hamburg .

Weiner, G and W. Liese 1990. Rattans-stem anatomy and taxonomic implications. lAWAn.s. 11 (I): 61-70.

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