Xylem Development at the Bases of Sprouts in the Branches of Ring-porous Species

この研究の目的は，環孔材樹種について，芽や葉の成長や樹冠量が樹幹での木部形成や木部の性質におよぼす影響を考察する基礎資料を得ることである．すなわち，常緑種1種と落葉樹5種の合計6種で，上部を切除した枝に萌芽を発生させ，萌芽の成長に伴う枝での木部形成の進行経過，新生木部細胞の二次壁形成および形成された道管の形状を観察し，樹冠での変化が木部形成経過と木部構造に与える影響を検討した．枝での木部形成は，萌芽の発生と成長が原因となって始まり，萌芽の基部から始まった木部形成は枝の下方へ向かって求基的に進行した．また，当年生木部の二次壁形成の進行は，道管とその周囲の細胞の二次壁形成が他の細胞よりも優先して進行し，通常の環孔材樹種の樹幹でみられる二次壁形成パターンと一致した．萌芽基部からの距離と道管形状との関係をアカメガシワとノダルミで調べた結果，接線（円周）方向には萌芽の真下から円周方向に離れるに伴い，管孔面積は減少する傾向を示したが，幹軸方向では管孔面積の変働係数がそれぞれ11％と8％であり，萌芽からの距離による影響は小さかった．当年生早材道管の大きさは，前年の早材道管よりも小さくなる傾向が認められ，樹冠の変化と道管の面積成長には密接な関係があることがわかった．また，前年の管孔面積に対する当年の管孔面積の割合は，散孔材樹種よりも道管径が大きい環孔材樹種で小さかった．The purpose of this study is to examine the relationship between crown development and cambial activity in the stem of broad-leaved trees. Hence the effects of sprouting on xylem formation at the decapitated branches of six ring-porous species (Table. 1) were examined. The results obtained were as follows : 1) The newly formed sprouts raised the cambial\u27activity in the decapitated branches, and the cambial activity initiated at the bases of the sprouts and extended toward the lower parts of the branches (Figs. 2-4). This result was the same as the result of diffuse-porous species. 2) In the branches of six species, the secondary cell wall formation initiated at vessels and extended toward a few of the surrounding cells(Fig. 5). There was no difference between the pattern of initiation of secondary cell wall formation in these six branches and the pattern in normal stem of ring-porous species. 3) In the branches of akamegashiwa (Mallotus japonicus) and nogurumi (Platycarya strobilacea), variations of single vessel area in tangential direction and mean vessel area in longitudinal direction were examined. As a result, it was recognized that in tangential direction, single vessel area decreased from directly below part of the sprout to opposite side, but in longitudinal direction, the coefficients of variation in mean vessel area were small (Figs.6 and 7). 4) Mean areas of earlywood vessels formed in the current year (V_c) and those in previous year (V_p) were measured, and the ratios of V_c to V_p were obtained in six species (Fig. 9). The results indicated thatV_c were smaller than V_p, and there was intact relationship between vessel enlargement and crown development in six species. And the values of V_c/V_p in ring-porous species were smaller than those in diffuse-porous species, because of larger V_p in ring-porous species than those in diffuse-porous species (Figs. 10-11)