Time Requirement for the Tracheid Differentiation in Softwoods Measured by the Inclination Date Marking

Abstract

針葉樹の仮道管が形成層帯で誕生してから, 発達した二次壁を完成して成熟するまでに必要とする時間を, スギ, ヒノキ, クロマツの6 - 9年生の若木で測定した。すなわちこれらの樹幹を定期的に, 短時間傾斜させることにより, 木部にかすかな圧縮あて材のデートマーキングを記録させ, ここから算出される仮道管生産速度と, 分化帯に含まれている仮道管の数を用いて分化過程に要する日数を求めた。スギにおいては, 放射方向の拡大に約3. 7日, S_1堆積に3. 7日, S_2堆積に8. 0日, S_3堆積に2. 8日, 二次壁の木化に4. 7日, 分化過程全体に合計約23日の値を得た。ヒノキでは同様の過程に, それぞれ2. 8, 2. 8, 7. 7, 2. 1, 2. 6日, 合計約18日の値を得た。クロマツについては, 一部のマーキングに失敗したが, 概略値として, 合計約22日となり, 3樹種の結果から, 針葉樹仮道管の分化にはおよそ3週間を必要とすることが明かとなった。

Date markings by the short period inclinations of a stem were attempted on the developing xylem of 6-9 year old trees of Cryptomeria japonica, Chamaecyparis obtusa and Pinus thunbergii. The increment of tracheid numbers during the growing season and the rate of tracheid production per one day were calculated by the date marker of faint compression wood arcs corresponding to the artificial inclination of stems. At the same time, the cell number contained in the differentiating xylem was examined in trees which had some date markers in April and May and were harvested in June. Using the number of tracheids contained in their developing stages and the rate of tracheid production, the time required for a tracheid differentiation was deduced. In the case of Cryptomeria, the time is as follows: about 3.7 days for the radial enlarging after the cell division; 3.7 days for the S1-deposition; 8.0 days for the S2-deposition; 2.8 days for the S3-deposition; 4.7 days for secondary wall lignification. The total time for the differentiation of a tracheid results in 23 days. In Chamaecyparis the times are 2.8, 2.8, 7.7, 2.1, and 2.6 days corresponding to the stages of radial enlargement, S1, S2, S3, and secondary wall lignification, respectively. The total one is 18 days. In Pinus the total time was only roughly estimated about 22 days because of missing of some date markers.