构树形成层的活动周期及其淀粉贮量的变化

PERIODICITY OF CAMBIAL ACTIVITY AND CHANGES OF STARCH CONTENT IN BROUSSONETIA PAPYRIFERA

在构树（Ｂｒｏｕｓｓｏｎｅｔｉａ ｐａｐｙｒｉｆｅｒａ （Ｌ．） Ｖｅｎｔ．）形成层活动周期中，每年７月末以后，未成熟的木质部和韧皮部逐渐减少，成熟的木质部和韧皮部急剧增多。８月初开始分化晚材。进入９月后木质部的形成逐渐停止，而一个半月以后才停止形成韧皮部。淀粉贮量的消长与形成层的活动周期有很强的相关关系。早春形成层恢复活动后，淀粉贮量逐渐减少直至消失。尔后，形成层活动减慢，特别是木质部分化停止后，淀粉又开始积累。当韧皮部分化也停止后，淀粉又消失，直至翌年１月才重新积累。

Methods of sampling and sections preparaction were the same as reported previously.Except that sampling was made at monthly intervals between May 20 and July 30, then at 7 14 day intervals between July 30 and October 14, and then at monthly intervals between October 14 and March 25 in the next year.The stored starch in various tissues was stained with PAS reaction.During active period of cambium in Broussonetia papyrifera after July 30, the cell layers of immature xylem and phloem decreased progressively, and the formation of mature xylem and phloem increased rapidly.The formation of late wood started early in August, formation of xylem ceased after September 5, followed by ceasation of phloem formation about 1 5 months later.Increasing and decreasing of stored starch were closely related to the periodicity of cambial activity during the year.Starch grains decreased progressively after cambial activity was resumed in early spring until they disappeared in all the stem tissues.Then, starch accumulated progressively again after cambial activity slowed down, particularly after the ceasation of xylem formation.However, after the formation of phloem had ceased, the stored starch once again disappeared progressively until the end of December, and accumulated again.Such changes might be related to the transition of cambium activity involving two periods of dormancy.