【摘要】 4月初,枫杨(Pterocarya stenoptera DC.)枝条形成层区韧皮部侧、以不分化状态越冬的一些细胞首先向韧皮部分化。4月中旬,形成层明显分裂,到11月初停止活动。每年产生5—11个纤维带及与之相间的筛管、伴胞和薄壁组织细胞带。4月中、下旬,形成层开始向木质部分化,完成分化的时间与韧皮部大致相同。韧皮部周年都有具功能的筛管。冬季到来时,当年产生的大部分筛管失去功能,但保留几个细胞宽的具功能筛管区,筛板孔开放,到5月中旬解体。10月,靠近形成层区产生数列部分分化的筛管分子,仍具细胞核,无P-蛋白质,已分裂出伴胞。它们于翌年4月成熟,7—9月解体。筛管寿命最长为8个月。冬季枝条具功能筛管较少,可能是云南紫胶虫在其上大量死亡的原因之一。更多还原

【Abstract】 Early in April of 1987, cells in an undifferentiated state which overwintered on the phloem side of the cambial zone in the branch of Pterocarya stenoptera began to differentiate into members of phloem. Cambium divided actively in mid-April and ceased to devide by early-November. Five to eleven bands of fibers alternating with the bands of sieve tubes, companion cells and phloem parenchyma cells produced every year. By mid to late April, new xylem differentiation began. Phloem and xylem differentiation ceased almost simultaneously. Functional sieve tube elements were present all the year round in the phloem. During winter, most sieve tubes produced in the current year ceased functioning, leaving only the zone of functional sieve tube of several rows of cells in width with open pores in the sieve plates. These sieve tubes did not collapse until mid-May. In October, several rows of partially differentiated sieve elements appeared near the cambial zone. They still possessed nuclei. The companion cells had produced but no P-protein. They matured during April of the following year and collapsed by July to September. The life span of sieve elements extended for 8 months at the most. In winter, there were less functional sieve tubes in the branch. This may be one of the reasons that only few Kerria yunnanensis survive on the branch of Pterocarya stenoptera.更多还原