两种麻黄根与茎次生木质部的解剖与进化和干旱环境的关系

用光镜及扫描电镜对两种麻黄根、茎次生木质部进行了解剖研究，结果表明：轴向系统主要由导管和管胞组成。横向系统由细胞壁木质化了的射线薄壁组织细胞组成。导管直径甚小，多孔式穿孔板，并存在导管与管胞之间的管状分子类型，推断麻黄属是裸子植物中最早出现导管的类群；管胞中有一些两头尖、胞腔小、具缘纹孔含纹孔塞的长分子，可视作纤维状管胞，使管胞的输导作用被削弱，而支持功能被加强；射线异型多列，已不具备裸子植物具较窄射线的特点。导管与管胞并存，恰好起到了一般沙生被子植物具宽窄两种类型的导管、复孔率高等典型的对干旱环境的适应特征的作用，茎中导管分子的长度和宽度均小于根，这与茎部需要较强的机械支持力相一致。

ANATOMY AND ADAPTABILITY TO DESERT ON ROOT AND STEM SECONDARY XYLEMS OF 2 PLANTS OF EPHEDRA

Secondary xylen structure of Ephedra przewalskii Stapf and E.intermedia Schrenk ex Meywas investigated by means of light and scanning electron microscopy.The axial system is chieflycomposed of tracheids and vessel elements.The horizontal system comprises the ray parenchymawith lignified cell walls.Vessel elements are very small in diameter,foramnate perforation plate.There are types of tracheary elements between tracheids and vessel elements,It is deduced thatEphedra may be the earliest group of plants with vessels in gymnosperm.Also present are manylong and narrow tracheid with tapered ends and Bordered pits with torus in the walls.If these tra-cheids may be considered as fibre-tracheids,transport function of tracheids is Whittle down andsupport function is emphasized.Two species with multiseriate ray have not had the feature withnarrow or uniseriate ray in gymnosperm.That narrow thacheids and wide vessels occur side byside playing just right the same role in narrow and wide vessel elements percentage of multiplevessels hign etc.typical features to adapt to xeric habitats of angiosperm growing in deserts.Thatlength and width of vessels in the stems are smaller than that of root in accordance with thatStems need stronger machanical strength in windy deserts environment.