Comparative Studies of Tracheary Element Structure of Some Gymnosperms with Angiosperms

Abstract

Tissues of the pinna and rachis of Cycas diannaensis and pinna, rachis, and root of Cycas taiwaniana, rachis of Cycas szechuanensis, stem of Metasequoia glyptostroboides (Taxodiaceae), stems of Chamaecyparis obtusa (Sieb.et Zucc.) Endl cv. Tetragona (Cupressaceae), and leaves and stems of Michelia alba and Michelia figo and stems of Amygdalus persica (angiosperms) were compared using the scanning electron microscopy. In all species of these gymnosperms, their many tracheary elemnts have perforations in end walls and lateral walls. These structures are the same as vessels of angiosperms; therefore, these tracheary elements are vessel elements. Many types of vessels were found in cycads: pitted vessels in M. glyptostroboides, spiral and pitted vessels in Chamaecyparis obtusa cv. Tetragona. The development and structural characteristics of vessels of cycads, the two other gymnosperms, and the angiosperms were identical. Some characters such as extent of incline of perforation plate in the end wall showed that vessel characters of some angiosperms were more primitive than the cycads or M. glyptostroboides and C. obtusa cv. Tetragona. Many of the vessel elements of the angiosperms were band shaped, without end walls, and had only two lateral walls and other two margins; the end was acuate or with an arc margin; the end of some vessel elements was acute with no perforations, many perforations located only in lateral wall. Such results are rarely reported in previous work. In all species, perforations were seen only in tracheae, and the walls of parenchyma cells only had a thin primary wall and without perforation. Analysis and discussion to the experimental measures which were observed and research of the structure of vessel or tracheid, pointed out that several measures all could be used and the Jeffrey’ method effects were better. Comparing the vessels of cycads, Taxodiaceae and Cupressaceae helps us to understand the mechanism in which these most primitive or more primitive extant gymnosperms were adapted to harsh environments and to understand these species’ evolutionary extent, and has the significance to the studies of plant anatomy, plant systematics and plant evolution.