ポプラの二次師部の構造

Abstract

ポプラの二次師部の発達経過および二次師部中での師管と師部放射組織の形態変化, さらには師部繊維の分化と壁層構造について観察し, 次の結果を得た。(1) 二次師部の分化は師管・柔細胞群に始まり, その後師部繊維群と師管・柔胞群が交互に分化し, 最後に師管・柔細胞群を分化して生長を終える傾向があった。(2) 休止期の形成層帯の師部側に, 分裂を行なった後生長を止めている細胞が認められた。これらの細胞は次の年に師管・柔細胞群に分化してゆくと考えられる。(3) 成熟した師管においても師板付近には常に核が認められた。(4) 師部放射組織は二次師部中でさまざまな形態変化を生じた。特にdilationが顕著であった。ほとんどのsclereidは放射組織細胞起源で, 師部繊維群と交差する部分の細胞から変化する傾向が認められた。(5) 師部繊維群は次に形成された師管・柔細胞群によって形成層から分離されたのち, 侵入生長を行なうと考えられる。生長休止期までにはすべての師部繊維は内腔がほとんどなくなるほどに肥厚していた。crystaliferous strandの分化は師部繊維群の分化と同時にその周縁で起った。(6) 偏光顕微鏡で見ると師部繊維壁に内外二層が認められ, フィブリル傾角は内層が30° - 40°, 外層が60° - 70°であった。

Development and differentiation of the secondary phloem and the morphological changes after maturation were studied in Populus euramericana GUINIER. Thin sections about 2 μ and 5 μ thick were taken from epoxy-embedded materials. The former sections were observed with Fujita's iodine staining method and the latter with safranin staining. 1) The secondary phloem developed in the alternate sequence from sieve tubes-parenchyma band (SP) to fibers band (F) (Photos 1, 2, 3, 4). Secondary phloem development usually began with SP differentiation and ended with SP differentiation. The number of fibers groups in a growth increment was variable, but there was a tendency that the first fibers group (F1) was wider and made a more continuous tangential band than later ones (F2, F3). Form these facts growth increments were distinguishable in the secondary phloem (Table 1). 2) In the dormant cambial zone, phloem cells which stopped further differentiation after an unequal cell division were observed (photo 5). It may be considered that these divided cells would differentiate into sieve elements and companion cells respectively, at the beggining of next spring. 3) Dense spherical nuclei were usually found in mature sieve elements, most frequently near the sieve plate, and they had different appearances from the nuclei in differentiating sieve elements (Photos 6, 7). In the dormant phloem the nuclei in mature sieve elments became swollen and dissolved (Photo 8). 4) Phloem rays changed their form considerably in different parts of the secondary phloem (Photos 7, 8, 9, 10). They dilated obviously in the outer part of the secondary phloem. Most of the sclereids originated from ray cells (Photos 10, 11). 5) After fiber primordia were separated from the cambium by the enlarging sieve tubes (Photo 2), they underwent intrusive elongation and matured within the growing season (Photo 3, 4). Phloem fibers groups were always surrounded by crystal-containing sclerified cells. 6) Phloem fiber walls were observed to be of two layers under the crossed nicols (Photo 10). The fibril angle of the inner layer measured by polarizing microscope was 30°to 40°, and that of the outer layer was 60°to 70° in the opposite direction to the inner layer.