TITLE	Anatomical characteristics of the secondary phloem in branches of Zelkova serrata Makino
AUTHOR	Ying-Shan HSU Department of Life Science Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Taiwan, Republic of China Shiang-Jiuun CHEN Department of Life Science Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Taiwan, Republic of China Chin-Mei LEE Division of Forest Utilization, Taiwan Forestry Research Institute, Taipei, Taiwan, Republic of China Ling-Long KUO-HUANG Department of Life Science Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Taiwan, Republic of China
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ABSTRACT	The properties and tissue compositions of reaction wood in the leaning trunks or branches of trees have been extensively investigated, but studies on the influence of the related reaction on the secondary phloem are few and incomplete. In this work, formation of the vascular and cork cambium and the secondary phloem in the upper and lower sides of branches of Zelkova serrata Makino were studied. Vascular cambium is formed first in the second internode of shoot. In the third internode, cork cambium began to initiate subepidermally, meanwhile two to four layers of grouped gelatinous fibers were first found in the cortex outside of all the primary phloem. Gelatinous fibers were also found in both the secondary xylem and secondary phloem. The leaning branches exhibited pronounced radial secondary growth promotion to the upper side, and the reaction wood formed eccentrically. The secondary phloem formed layers of conducting sieve elements alternately with gelatinous fibers. Comparing the secondary phloem in the upper side (reaction phloem) of the branches with that in the lower side (opposite phloem), there is no obvious difference in thickness. Nevertheless, it was found that in the cross sections, the gelatinous fibers formed earlier, and there were more continuous cell seriates and a much larger area ratio in the upper side. Besides, the sieve tubes in the upper side of secondary phloem were longer and wider and possessed a very horizontally-orientated sieve plate between two sieve elements. These features may imply that, in branches of Zelkova serrata, the secondary phloem of the upper side (reaction phloem) may have a higher translocation efficiency.
KEYWORD	Branches; Gelatinous fibers; Reaction phloem; Secondary phloem; Zelkova serrata;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 46 Number 2 April 2005, page 143-149, 7 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China