ヤマザクラとマカンバ乾燥材の空隙構造

Abstract

広葉樹散孔材の流動通路の定量的情報を得るため, 道管せん孔を異にするヤマザクラとマカンバについて, 顕微鏡法を援用して水銀圧入法で永久空隙構造を検討した。両樹種の永久空隙は水銀圧入曲線 (Figs. 3, 4) からミクロ, サブマクロおよびマクロ空隙に区分できる。半径0. 05 - 0. 08μm以下のミクロ空隙の容積が全空隙の14, 29％にも達することから, この空隙に無孔の壁孔膜を通って圧入される放射組織細胞内こうと細胞壁の微小空隙が帰属するとおもわれる。半径3μm以下のサブマクロな空隙は, それに対応する圧入曲線部分が木口試験片の厚きで異なることから, 壁孔対を通って圧入される木部繊維などの内こうに相当するとおもわれる。半径5μm以上のマクロ空隙は全空隙容積の20 - 25％を占める道管のほかに, 試験片木口で閉口する木部繊維などの2. 4 - 3. 4％の内こうを含む (Figs. 5, 6)。細孔分布曲線のピークは顕微鏡法に比べて水銀圧入法ではヤマザクラで5 - 10μm, マカンバで25 - 30μmそれぞれ小径側にずれる (Figs. 7, 8)。これはそれぞれ単せん孔および階段せん孔による水銀圧入に対するボトルネック効果によるものである。

In order to obtain some quantitative information on the flow paths of hardwood, the structures of permanent pores in wood have been investigated for the species with different vessel perforations such as Yamazakura (Prunus jamasakura OHWI) and Makanba (Betula maximowicziana REGEL) by the mercury porosimetry and the microscopic method. It is obvious from the pressuring curve (Figs.3 and 4) obtained by the mercury porosimetry that the permanent pores in both the wood species can be classified into micro-, submacro- and macropores, depending upon the pore size. Since the micropores with less than 0.05~0.08μm radius contribute 14 or 29% to the total pore volume, they are assigned to the lumen of ray cell penetrating the pit membrane as well as the fine pores in cell wall. The submacropores having the radius of less than 3μm can be assigned to the lumen of wood fiber being connected through pit-pairs, because of the corresponding parts of pressuring curves depend on the thickness of wood specimen. The macropores having radius more than 5μm include the opening of the lumen of wood fibers at the cross section which share 2.4~3.4% of the total pore volume in addition to the lumen of vessel sharing 20~25% of whole pores (Figs.5 and 6). The peak position of the pore size distribution curve obtained by the mercury porosimetry shifts to the smaller radius by 5~10μm in the case of Yamazakura, and by 25-30μm in the case of Makanba, compared to that obtained by microscopic method (Figs. 7 and 8). This is caused from the difference in the bottle-neck cffect on pressuring for simple perforation (Yamazakura) and scalariform perforation (Makanba), respectively.